Fix: Don't use a timer for hundredth tick determination

src/window_gui.h

@@ -691,7 +691,9 @@ public:
 	virtual void OnGameTick() {}
 
 	/**
-	 * Called once every 100 (game) ticks.
+	 * Called once every 100 (game) ticks, or once every 3s, whichever comes last.
+	 * In normal game speed the frequency is 1 call every 100 ticks (can be more than 3s).
+	 * In fast-forward the frequency is 1 call every ~3s (can be more than 100 ticks).
 	 */
 	virtual void OnHundredthTick() {}