fix #323,preserve compatibility with plasma 5.8

plasmoid/contents/ui/main.qml

@@ -446,33 +446,24 @@ Item {
         }
     }
 
-    //! TaskManagerBackend required a groupDialog setting otherwise it crashes. This patch
-    //! sets one just in order not to crash TaskManagerBackend
-    PlasmaCore.Dialog {
-        //ghost group Dialog to not crash TaskManagerBackend
-        id: groupDialog
-        visible: false
-
-        type: PlasmaCore.Dialog.PopupMenu
-        flags: Qt.WindowStaysOnTopHint
-        hideOnWindowDeactivate: true
-        location: plasmoid.location
-    }
-
     TaskManagerApplet.Backend {
         id: backend
 
         taskManagerItem: root
         toolTipItem: toolTipDelegate
-        groupDialog: groupDialog
-        //! there is a conflict between preview windows and highlight effect, it creates
-        //! a crash when both are activated during hovering. So we enable in each case
-        //! only one of both
         highlightWindows: root.highlightWindows
 
         onAddLauncher: {
             tasksModel.requestAddLauncher(url);
         }
+
+        Component.onCompleted: {
+            //! In Plasma 5.9 TaskManagerBackend required a groupDialog setting
+            //! otherwise it crashes.
+            if (groupDialog) {
+                groupDialog = undefined;
+            }
+        }
     }
 
     TaskManagerApplet.DragHelper {