Fix some PHP 8.1 "strlen(null)" exceptions which block rendering a project page

Summary:
`strlen()` was used in Phabricator to check if a generic value is a non-empty string.
This behavior is deprecated since PHP 8.1. Phorge adopts `phutil_nonempty_string()` as a replacement.

Note: this may highlight other absurd input values that might be worth correcting
instead of just ignoring. If phutil_nonempty_string() throws an exception in your
instance, report it to Phorge to evaluate and fix that specific corner case.

Closes T15313

Test Plan:
Applied these three changes (with D25144, D25145, D25146, D25147, D25151,
D25152, D25153 on top).
Afterwards end up with the unresolved exception covered by T15263.

Reviewers: O1 Blessed Committers, valerio.bozzolan

Reviewed By: O1 Blessed Committers, valerio.bozzolan

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

Maniphest Tasks: T15313

Differential Revision: https://we.phorge.it/D25163

src/applications/project/state/PhabricatorWorkboardViewState.php

···
       $this->requestState['filter'] = $request->getStr('filter');
     }
 
-    if (strlen($request->getURIData('queryKey'))) {
+    if (phutil_nonempty_string($request->getURIData('queryKey'))) {
       $this->requestState['filter'] = $request->getURIData('queryKey');
     }
 
···
 
   public function getQueryKey() {
     $request_query = idx($this->requestState, 'filter');
-    if (strlen($request_query)) {
+    if (phutil_nonempty_string($request_query)) {
       return $request_query;
     }
 
···
 
     $default_query = $project->getDefaultWorkboardFilter();
 
-    if (strlen($default_query)) {
+    if (phutil_nonempty_string($default_query)) {
       return $default_query;
     }