QmlDesigner: Check if model has parent property

If you compare the parent property you must check if there is one.

Task-number: QTCREATORBUG-12599
Change-Id: I6033a7572f307d2fd11e90c95cbb7515ef8dcca0
Reviewed-by: Tim Jenssen <tim.jenssen@digia.com>

src/plugins/qmldesigner/components/navigator/navigatortreemodel.cpp

@@ -623,7 +623,7 @@ static bool isInLayoutable(NodeAbstractProperty &parentProperty)
 
 static void reparentModelNodeToNodeProperty(NodeAbstractProperty &parentProperty, const ModelNode &modelNode)
 {
-    if (parentProperty != modelNode.parentProperty()) {
+    if (!modelNode.hasParentProperty() || parentProperty != modelNode.parentProperty()) {
         if (isInLayoutable(parentProperty)) {
             removePosition(modelNode);
             parentProperty.reparentHere(modelNode);