[Notifications] Don't invoke default action on drag if we're dragging

Otherwise dragging a screenshot off a notification will immediately
trigger the default action.

applets/notifications/package/contents/ui/NotificationPopup.qml

@@ -117,7 +117,7 @@ PlasmaCore.Dialog {
         DropArea {
             anchors.fill: parent
             onEntered: {
-                if (notificationPopup.hasDefaultAction) {
+                if (notificationPopup.hasDefaultAction && !notificationItem.dragging) {
                     dragActivationTimer.start();
                 } else {
                     drag.accepted = false;