QmlDesigner: Fix glitch in Add TabBar

With Qt 5.9 we have to first anchor the TabBar.
Otherwise the tab buttons are not layouted properly.

Change-Id: Ia20f2f6bbe8659f3b0be36ae3b56e8ce07b2dca1
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/plugins/qmldesigner/components/componentcore/modelnodeoperations.cpp

@@ -987,6 +987,12 @@ void addTabBarToStackedContainer(const SelectionContext &selectionContext)
 
         const int maxValue = container.directSubModelNodes().count();
 
+        QmlItemNode tabBarItem(tabBarNode);
+
+        tabBarItem.anchors().setAnchor(AnchorLineLeft, containerItemNode, AnchorLineLeft);
+        tabBarItem.anchors().setAnchor(AnchorLineRight, containerItemNode, AnchorLineRight);
+        tabBarItem.anchors().setAnchor(AnchorLineBottom, containerItemNode, AnchorLineTop);
+
         for (int i = 0; i < maxValue; ++i) {
             ModelNode tabButtonNode =
                     view->createModelNode("QtQuick.Controls.TabButton",
@@ -997,12 +1003,6 @@ void addTabBarToStackedContainer(const SelectionContext &selectionContext)
             tabBarNode.defaultNodeListProperty().reparentHere(tabButtonNode);
         }
 
-        QmlItemNode tabBarItem(tabBarNode);
-
-        tabBarItem.anchors().setAnchor(AnchorLineLeft, containerItemNode, AnchorLineLeft);
-        tabBarItem.anchors().setAnchor(AnchorLineRight, containerItemNode, AnchorLineRight);
-        tabBarItem.anchors().setAnchor(AnchorLineBottom, containerItemNode, AnchorLineTop);
-
         const QString id = tabBarNode.validId();
 
         container.removeProperty(indexPropertyName);