Fix GUI2 dialogs undrawing themselves on the wrong position

This relies on the draw-layering instead to restore the windows. With
the undrawing it will leave unsightly black artefacts or draw over
otherwise updated graphics, causing undesired visual effects.

src/gui/dialogs/dialog.hpp

@@ -134,7 +134,7 @@ public:
 		, always_save_fields_(false)
 		, fields_()
 		, focus_()
-		, restore_(true)
+		, restore_(false)
 	{
 	}