Fix GetNamedWidget() always returning the last valid widget

This is problematic when doing different logic when a widget doesn't exist, for example when loading a map, if the continue button doesn't exist then the game should continue automatically

code/uilib/uimenu.cpp

@@ -291,7 +291,7 @@ UIWidget *Menu::GetNamedWidget
 		}
 	}
 
-	return pWidget;
+	return NULL;
 }
 
 void Menu::Update