Add: data parameter in Window::Close method.

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

src/error_gui.cpp

@@ -313,7 +313,7 @@ public:
 		if (_right_button_down && !this->is_critical) this->Close();
 	}
 
-	void Close() override
+	void Close([[maybe_unused]] int data = 0) override
 	{
 		SetRedErrorSquare(INVALID_TILE);
 		if (_window_system_initialized) ShowFirstError();