Codechange: Set specific widgets dirty instead of window.

(cherry picked from commit 8321ef0061)

src/window.cpp

@@ -2470,8 +2470,8 @@ static EventState HandleActiveWidget()
 		if (w->mouse_capture_widget >= 0) {
 			/* Abort if no button is clicked any more. */
 			if (!_left_button_down) {
+				w->SetWidgetDirty(w->mouse_capture_widget);
 				w->mouse_capture_widget = -1;
-				w->SetDirty();
 				return ES_HANDLED;
 			}