Fix 91b8ce07: dedicated servers could no longer create screenshots (#9232)

Although most commands are not useful on a dedicated server,
screenshot commands should be dequeued.

src/video/dedicated_v.cpp

@@ -270,6 +270,7 @@ void VideoDriver_Dedicated::MainLoop()
 
 	while (!_exit_game) {
 		if (!_dedicated_forks) DedicatedHandleKeyInput();
+		this->DrainCommandQueue();
 
 		ChangeGameSpeed(_ddc_fastforward);
 		this->Tick();

src/video/video_driver.hpp

@@ -319,23 +319,6 @@ protected:
 		return std::chrono::microseconds(1000000 / _settings_client.gui.refresh_rate);
 	}
 
-	std::chrono::steady_clock::time_point next_game_tick;
-	std::chrono::steady_clock::time_point next_draw_tick;
-
-	bool fast_forward_key_pressed; ///< The fast-forward key is being pressed.
-	bool fast_forward_via_key; ///< The fast-forward was enabled by key press.
-
-	bool is_game_threaded;
-	std::thread game_thread;
-	std::mutex game_state_mutex;
-	std::mutex game_thread_wait_mutex;
-
-	static void GameThreadThunk(VideoDriver *drv);
-
-private:
-	std::mutex cmd_queue_mutex;
-	std::vector<std::function<void()>> cmd_queue;
-
 	/** Execute all queued commands. */
 	void DrainCommandQueue()
 	{
@@ -354,6 +337,23 @@ private:
 		}
 	}
 
+	std::chrono::steady_clock::time_point next_game_tick;
+	std::chrono::steady_clock::time_point next_draw_tick;
+
+	bool fast_forward_key_pressed; ///< The fast-forward key is being pressed.
+	bool fast_forward_via_key; ///< The fast-forward was enabled by key press.
+
+	bool is_game_threaded;
+	std::thread game_thread;
+	std::mutex game_state_mutex;
+	std::mutex game_thread_wait_mutex;
+
+	static void GameThreadThunk(VideoDriver *drv);
+
+private:
+	std::mutex cmd_queue_mutex;
+	std::vector<std::function<void()>> cmd_queue;
+
 	void GameLoop();
 	void GameThread();
 };