Fix bug introduced in previous commit (rev 1.402) of this file:

The js_finalize_queue() is eventually called when garbage is collected and
js_finalize_queue() calls msgQueueDetach(), so bg-load()s did not "leak"
semaphores and this "fix" actually introduced a problem where the queue was
detached too many times, leaving the ref count 0 while there was actually
a lingering reference (in the parent), leading to a crash as reported by echto
(thanks, echto!).

src/sbbs3/js_global.c

@@ -151,7 +151,6 @@ static void background_thread(void* arg)
 
 	jsrt_Release(bg->runtime);
 	sem_post(bg->sem);
-	msgQueueDetach(bg->msg_queue);
 	free(bg);
 }