Fix comparing an array in a conditional, which is always true

Instead, check the intent of the original code, if the `szImg` string is
not empty.

Signed-off-by: Chris Burel <burelc@amazon.com>

Code/Framework/AzCore/Platform/Windows/AzCore/Debug/StackTracer_Windows.cpp

@@ -596,7 +596,7 @@ namespace AZ {
                 result = GetLastError();
             }
             ULONGLONG fileVersion = 0;
-            if (szImg != NULL)
+            if (szImg[0]) // !szImg.empty()
             {
                 // try to retrieve the file-version:
                 VS_FIXEDFILEINFO* fInfo = NULL;