[KMTEST] Fix 3 Clang-Cl warnings about Status and Callbacks (#502)

* 1 "warning: variable 'Status' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]"
* 2 "warning: comparison of unsigned expression < 0 is always false [-Wtautological-unsigned-zero-compare]"
* Use a consistent type for "i" and fix a comment
* Also update licence header.

CORE-14306

modules/rostests/kmtests/kmtest_drv/kmtest_fsminifilter.c

···
 /*
- * PROJECT:         ReactOS kernel-mode tests - Filter Manager
- * LICENSE:         GPLv2+ - See COPYING in the top level directory
- * PURPOSE:         FS Mini-filter wrapper to host the filter manager tests
- * PROGRAMMER:      Thomas Faber <[e-mail]>
- *                  Ged Murphy <[e-mail]>
+ * PROJECT:     ReactOS kernel-mode tests - Filter Manager
+ * LICENSE:     GPL-2.0+ (https://spdx.org/licenses/GPL-2.0+)
+ * PURPOSE:     FS Mini-filter wrapper to host the filter manager tests
+ * COPYRIGHT:   Copyright 2017 Thomas Faber <[e-mail]>
+ *              Copyright 2017 Ged Murphy <[e-mail]>
  */
 
 #include <ntifs.h>
···
 static PDEVICE_OBJECT KmtestDeviceObject;
 static FILTER_DATA FilterData;
 static PFLT_OPERATION_REGISTRATION Callbacks = NULL;
+static ULONG CallbacksCount = 0;
 static PFLT_CONTEXT_REGISTRATION Contexts = NULL;
 
 static PFLT_CONNECT_NOTIFY FilterConnect = NULL;
···
     {
         ExFreePoolWithTag(Callbacks, KMTEST_FILTER_POOL_TAG);
         Callbacks = NULL;
+        CallbacksCount = 0;
     }
 
     return STATUS_SUCCESS;
···
     UNICODE_STRING VolumeName;
     ULONG ReportedSectorSize = 0;
     ULONG SectorSize = 0;
-    NTSTATUS Status;
+    NTSTATUS Status = STATUS_SUCCESS;
 
     PAGED_CODE();
 
···
     _In_ CONST FLT_OPERATION_REGISTRATION *OperationRegistration)
 {
     ULONG Count = 0;
-    INT i;
+    ULONG i;
 
     if (Callbacks)
     {
···
         return STATUS_INSUFFICIENT_RESOURCES;
     }
 
-    /* Copy the array, but using the our own pre/post callbacks */
+    /* Copy the array, but using our own pre/post callbacks */
     for (i = 0; i < Count; i++)
     {
         Callbacks[i].MajorFunction = OperationRegistration[i].MajorFunction;
···
 
     /* Terminate the array */
     Callbacks[Count].MajorFunction = IRP_MJ_OPERATION_END;
+
+    /* Save the count of IRPs, not counting IRP_MJ_OPERATION_END last entry */
+    CallbacksCount = Count;
 
     return STATUS_SUCCESS;
 }
···
 {
     FLT_PREOP_CALLBACK_STATUS Status;
     UCHAR MajorFunction;
-    INT i;
+    ULONG i;
 
     Status = FLT_PREOP_SUCCESS_NO_CALLBACK;
     MajorFunction = Data->Iopb->MajorFunction;
 
-    for (i = 0; i < sizeof(Callbacks) / sizeof(Callbacks[0]); i++)
+    for (i = 0; i < CallbacksCount; i++)
     {
         if (MajorFunction == Callbacks[i].MajorFunction)
         {
···
 {
     FLT_POSTOP_CALLBACK_STATUS Status;
     UCHAR MajorFunction;
-    INT i;
+    ULONG i;
 
     Status = FLT_POSTOP_FINISHED_PROCESSING;
     MajorFunction = Data->Iopb->MajorFunction;
 
-    for (i = 0; i < sizeof(Callbacks) / sizeof(Callbacks[0]); i++)
+    for (i = 0; i < CallbacksCount; i++)
     {
         if (MajorFunction == Callbacks[i].MajorFunction)
         {