Add: data parameter in Window::Close method.

This allows passing data when closing a window, e.g. to indicate how it was closed.

src/fios_gui.cpp

@@ -399,7 +399,7 @@ public:
 		}
 	}
 
-	void Close() override
+	void Close([[maybe_unused]] int data = 0) override
 	{
 		/* pause is only used in single-player, non-editor mode, non menu mode */
 		if (!_networking && _game_mode != GM_EDITOR && _game_mode != GM_MENU) {