applets/taskmanager: Move some childCountChanged code from Task to GroupDialog

applets/taskmanager/package/contents/ui/GroupDialog.qml

@@ -121,7 +121,13 @@ PlasmaCore.Dialog {
 
                 reuseItems: false
 
-                onCountChanged: if (count > 0) backend.cancelHighlightWindows()
+                onCountChanged: {
+                    if (count > 0) {
+                        backend.cancelHighlightWindows()
+                    } else {
+                        groupDialog.visible = false;
+                    }
+                }
             }
         }
     }

applets/taskmanager/package/contents/ui/Task.qml

@@ -93,16 +93,6 @@ MouseArea {
     }
 
     onChildCountChanged: {
-        if (!childCount && groupDialog.visualParent == task) {
-            groupDialog.visible = false;
-
-            return;
-        }
-
-        if (containsMouse) {
-            groupDialog.activeTask = null;
-        }
-
         if (childCount > previousChildCount) {
             tasksModel.requestPublishDelegateGeometry(modelIndex(), backend.globalRect(task), task);
         }