Don't loop Cef exit while shutting down if task post fails

If the `manager_thread` exits early, there will be no message loop to
post the task to, and a permanent deadlock would occur. Rather than
guaranteeing a deadlock, this at least lowers the odds of one.

A future implementation might be more aware of the run state of the
manager thread and handle these exit scenarios more explicitly.

Author: tt2468

obs-browser-plugin.cpp

@@ -779,8 +779,8 @@ void obs_module_unload(void)
 	BrowserShutdown();
 #else
 	if (manager_thread.joinable()) {
-		while (!QueueCEFTask([]() { CefQuitMessageLoop(); }))
-			os_sleep_ms(5);
+		if (!QueueCEFTask([]() { CefQuitMessageLoop(); }))
+			blog(LOG_DEBUG, "[obs-browser]: Failed to post CefQuit task to loop");
 
 		manager_thread.join();
 	}