Fix: race-condition when quitting the game with libcurl (#11688)

There could be a callback in _new_http_callbacks that is not
processed yet. All callbacks in _http_callbacks were cancelled,
but not the ones in _new_http_callbacks

src/network/core/http_curl.cpp

@@ -278,10 +278,9 @@ void NetworkHTTPUninitialize()
 {
 	_http_thread_exit = true;
 
-	/* Queues must be cleared (and the queue CV signalled) after _http_thread_exit is set to ensure that the HTTP thread can exit */
-	for (auto &callback : _http_callbacks) {
-		callback->ClearQueue();
-	}
+	/* Ensure the callbacks are handled. This is mostly needed as we send
+	 * a survey just before close, and that might be pending here. */
+	NetworkHTTPSocketHandler::HTTPReceive();
 
 	{
 		std::lock_guard<std::mutex> lock(_http_mutex);

src/network/core/http_shared.h

@@ -97,20 +97,6 @@ public:
 		return this->queue.empty();
 	}
 
-
-	/**
-	 * Clear everything in the queue.
-	 *
-	 * Should be called from the Game Thread.
-	 */
-	void ClearQueue()
-	{
-		std::lock_guard<std::mutex> lock(this->mutex);
-
-		this->queue.clear();
-		this->queue_cv.notify_all();
-	}
-
 	HTTPThreadSafeCallback(HTTPCallback *callback) : callback(callback) {}
 
 	~HTTPThreadSafeCallback()