Use Window iterate instead of from front/back when no order required

src/openttd.cpp

@@ -527,7 +527,7 @@ static void ShutdownGame()
 static void LoadIntroGame(bool load_newgrfs = true)
 {
 	UnshowCriticalError();
-	for (Window *w : Window::IterateFromFront()) {
+	for (Window *w : Window::Iterate()) {
 		w->Close();
 	}