Fix usage of TerminateThread() causing critical section corruption.

This patch was submitted to the GIMP project by a publisher wishing to
keep confidentiality (hence anonymously). I just pass along the patch.
Here is the patch explanation which came with:

First they remind us what Microsoft documentation says about
TerminateThread:
> TerminateThread is a dangerous function that should only be used in
> the most extreme cases. You should call TerminateThread only if you
> know exactly what the target thread is doing, and you control all of
> the code that the target thread could possibly be running at the time
> of the termination.
(https://docs.microsoft.com/en-us/windows/win32/api/processthreadsapi/nf-processthreadsapi-terminatethread)

Then they say that 5 milliseconds time-out might not be long enough for
the thread to exit gracefully. They propose to set it to a much higher
value (for instance here 5 seconds).

And finally you should always check the return value of
WaitForSingleObject(). In particular you want to run TerminateThread()
only if WaitForSingleObject() failed, not on success case.

driver/others/blas_server_win32.c

@@ -462,11 +462,15 @@ int BLASFUNC(blas_thread_shutdown)(void){
 
     for(i = 0; i < blas_num_threads - 1; i++){
       // Could also just use WaitForMultipleObjects
-      WaitForSingleObject(blas_threads[i], 5);  //INFINITE);
+      DWORD wait_thread_value = WaitForSingleObject(blas_threads[i], 5000);
+
 #ifndef OS_WINDOWSSTORE
-// TerminateThread is only available with WINAPI_DESKTOP and WINAPI_SYSTEM not WINAPI_APP in UWP
-      TerminateThread(blas_threads[i],0);
+      // TerminateThread is only available with WINAPI_DESKTOP and WINAPI_SYSTEM not WINAPI_APP in UWP
+      if (WAIT_OBJECT_0 != wait_thread_value) {
+        TerminateThread(blas_threads[i],0);
+      }
 #endif
+
       CloseHandle(blas_threads[i]);
     }