Fix some potentially undefined variables

Summary:
Fix 17 trivial "Variable might not be defined" issues found by PHPStan static code analysis to have a little bit less noise (there are many more which makes it harder to find real problems). Defensive programming yadda yadda.

```
Line src/applications/people/controller/PhabricatorPeopleInviteSendController.php
136 Variable $actions might not be defined.
146 Variable $any_valid might not be defined.
Line src/applications/phid/query/PhabricatorObjectListQuery.php
203 Variable $suffix_map might not be defined.
Line src/applications/search/engine/PhabricatorProfileMenuEngine.php
420 Variable $builtins might not be defined.
Line support/startup/PhabricatorClientLimit.php
204 Variable $bucket might not be defined.
241 Variable $min might not be defined.
Line src/view/phui/PHUIRemarkupPreviewPanel.php
114 Variable $content might not be defined.
Line src/view/phui/PHUIInfoView.php
109 Variable $icon might not be defined.
Line src/view/phui/PHUICurtainObjectRefView.php
237 Variable $icon_view might not be defined.
Line src/applications/maniphest/conduit/ManiphestConduitAPIMethod.php
161 Variable $comments might not be defined.
Line src/applications/people/typeahead/PhabricatorPeopleDatasource.php
75 Variable $handles might not be defined.
Line src/applications/settings/controller/PhabricatorSettingsMainController.php
117 Variable $user might not be defined.
Line src/applications/files/engine/PhabricatorFileStorageEngine.php
327 Variable $engine might not be defined.
Line src/infrastructure/cache/PhutilAPCKeyValueCache.php
33 Variable $result might not be defined.
Line src/applications/config/engine/PhabricatorSetupEngine.php
50 Variable $issue might not be defined.
Line src/applications/diffusion/management/DiffusionRepositoryStorageManagementPanel.php
314 Variable $refs might not be defined.
Line src/applications/diffusion/DiffusionLintSaveRunner.php
123 Variable $all_files might not be defined.
```

Test Plan: Read the code; run static code analysis before and after.

Reviewers: O1 Blessed Committers, mainframe98

Reviewed By: O1 Blessed Committers, mainframe98

Subscribers: mainframe98, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Differential Revision: https://we.phorge.it/D26198

src/applications/config/engine/PhabricatorSetupEngine.php

···
       // because data may be at risk.
       PhabricatorSetupCheck::resetSetupState();
 
-      return PhabricatorSetupCheck::newIssueResponse($issue);
+      return PhabricatorSetupCheck::newIssueResponse($fatal_issue);
     }
 
     $issue_keys = PhabricatorSetupCheck::getUnignoredIssueKeys($issues);

src/applications/diffusion/DiffusionLintSaveRunner.php

···
       $this->lintCommit = $this->branch->getLintCommit();
     }
 
+    $all_files = array();
     if ($this->lintCommit) {
       try {
         $commit = $this->lintCommit;

src/applications/diffusion/management/DiffusionRepositoryStorageManagementPanel.php

···
     $viewer = $this->getViewer();
 
     $caught = null;
+    $refs = array();
+
     try {
       $refs = $repository->getAlmanacServiceRefs($viewer, $options);
     } catch (Exception $ex) {
···
 
     $info_view = null;
     if ($caught) {
-      $refs = array();
       $info_view = id(new PHUIInfoView())
         ->setErrors(
           array(

src/applications/files/engine/PhabricatorFileStorageEngine.php

···
       }
     }
 
-    if (!$min) {
+    if (!$min || !isset($engine)) {
       return null;
     }
 

src/applications/maniphest/conduit/ManiphestConduitAPIMethod.php

···
     foreach ($changes as $type => $value) {
       $transaction = clone $template;
       $transaction->setTransactionType($type);
-      if ($type == PhabricatorTransactions::TYPE_COMMENT) {
+      if ($type == PhabricatorTransactions::TYPE_COMMENT &&
+          isset($comments)) {
         $transaction->attachComment(
           id(new ManiphestTransactionComment())
             ->setContent($comments));

src/applications/people/controller/PhabricatorPeopleInviteSendController.php

···
     $message = $request->getStr('message');
     $emails = $request->getStr('emails');
     $severity = PHUIInfoView::SEVERITY_ERROR;
+
+    $any_valid = false;
+    $all_valid = true;
+    $actions = null;
+
     if ($request->isFormPost()) {
       // NOTE: We aren't using spaces as a delimiter here because email
       // addresses with names often include spaces.
···
           $viewer,
           $email_list);
 
-        $any_valid = false;
-        $all_valid = true;
         foreach ($actions as $action) {
           if ($action->willSend()) {
             $any_valid = true;

src/applications/people/typeahead/PhabricatorPeopleDatasource.php

···
     $users = $this->executeQuery($query);
 
     $is_browse = $this->getIsBrowse();
+    $handles = array();
 
     if ($is_browse && $users) {
       $phids = mpull($users, 'getPHID');

src/applications/phid/query/PhabricatorObjectListQuery.php

···
     // If we're parsing with suffixes, strip them off any tokens and keep
     // track of them for later.
     $suffixes = $this->getSuffixes();
+    $suffix_map = array();
     if ($suffixes) {
       $suffixes = array_fuse($suffixes);
-      $suffix_map = array();
       $stripped_map = array();
       foreach ($name_map as $key => $name) {
         $found_suffixes = array();

src/applications/search/engine/PhabricatorProfileMenuEngine.php

···
 
   private function loadBuiltinProfileItems($mode) {
     $object = $this->getProfileObject();
+    $builtins = array();
 
     switch ($mode) {
       case self::MODE_GLOBAL:
···
           $this->getCustomPHID());
         break;
       case self::MODE_COMBINED:
-        $builtins = array();
         $builtins[] = $this->getBuiltinCustomProfileItems(
           $object,
           $this->getCustomPHID());

src/applications/settings/controller/PhabricatorSettingsMainController.php

···
     $crumbs->addTextCrumb($panel->getPanelName());
     $crumbs->setBorder(true);
 
-    if ($this->user) {
+    if (isset($user)) {
       $header_text = pht('Edit Settings: %s', $user->getUserName());
     } else {
       $header_text = pht('Edit Global Settings');

src/infrastructure/cache/PhutilAPCKeyValueCache.php

···
     $results = array();
     $fetched = false;
     foreach ($keys as $key) {
-      if ($is_apcu) {
-        $result = apcu_fetch($key, $fetched);
+      if (!$is_apcu) {
+        continue;
       }
-
+      $result = apcu_fetch($key, $fetched);
       if ($fetched) {
         $results[$key] = $result;
       }

src/view/phui/PHUICurtainObjectRefView.php

···
   }
 
   private function newIconView() {
+    $icon_view = null;
     $handle = $this->handle;
 
     if ($handle) {

src/view/phui/PHUIInfoView.php

···
       return $this->icon;
     }
 
+    $icon = null;
     switch ($this->getSeverity()) {
       case self::SEVERITY_ERROR:
         $icon = 'fa-exclamation-circle';

src/view/phui/PHUIRemarkupPreviewPanel.php

···
       ),
       $loading);
 
+    $content = null;
     if (!$this->previewType) {
       $header = null;
       if ($this->header) {

support/startup/PhabricatorClientLimit.php

···
       $bucket = apcu_fetch($bucket_key);
     }
 
-    if (!is_array($bucket)) {
+    if (!isset($bucket) || !is_array($bucket)) {
       $bucket = array();
     }
 
···
     // If we don't have any buckets stored yet, store the current bucket as
     // the oldest bucket.
     $cur = $this->getCurrentBucketID();
-    if (!$min) {
+    if (!isset($min) || !$min) {
       if ($is_apcu) {
         @apcu_store($min_key, $cur);
       }