QmlDesigner: Don't set anchors for the root item

Task-number: QTCREATORBUG-11800
Change-Id: I6d23b23f250ccef76c7b9182071770a4f4f490f7
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>

share/qtcreator/qml/qmlpuppet/qml2puppet/instances/graphicalnodeinstance.cpp

@@ -372,6 +372,9 @@ void GraphicalNodeInstance::setPropertyBinding(const PropertyName &name, const Q
     if (name == "state")
         return; // states are only set by us
 
+    if (name.startsWith("anchors.") && isRootNodeInstance())
+        return;
+
     ObjectNodeInstance::setPropertyBinding(name, expression);
 
     quickItem()->update();