Add: data parameter in Window::Close method.

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

src/smallmap_gui.h

@@ -199,7 +199,7 @@ public:
 	void SmallMapCenterOnCurrentPos();
 	Point GetStationMiddle(const Station *st) const;
 
-	void Close() override;
+	void Close([[maybe_unused]] int data = 0) override;
 	void SetStringParameters(int widget) const override;
 	void OnInit() override;
 	void OnPaint() override;