coreaudio: Flush/stop the AudioQueue before disposing of it.

Otherwise, a CoreAudio thread lingers forever, and coreaudiod eats CPU
until the SDL process terminates.

Fixes #7689.

src/audio/coreaudio/SDL_coreaudio.m

@@ -692,6 +692,8 @@ static void COREAUDIO_CloseDevice(_THIS)
 
     /* dispose of the audio queue before waiting on the thread, or it might stall for a long time! */
     if (this->hidden->audioQueue) {
+        AudioQueueFlush(this->hidden->audioQueue);
+        AudioQueueStop(this->hidden->audioQueue, 0);
         AudioQueueDispose(this->hidden->audioQueue, 0);
     }