Fix: no fast forward in network was ensured only from GUI side (#11206)

(cherry picked from commit 2bf3c02fbf)

src/toolbar_gui.cpp

@@ -298,6 +298,8 @@ static CallBackFunction ToolbarPauseClick(Window *w)
  */
 static CallBackFunction ToolbarFastForwardClick(Window *w)
 {
+	if (_networking) return CBF_NONE; // no fast forward in network game
+
 	ChangeGameSpeed(_game_speed == 100);
 
 	if (_settings_client.sound.click_beep) SndPlayFx(SND_15_BEEP);