QmlDesigner.NodeInstances: Fix id getter

Add getter for id in node instances.

src/plugins/qmldesigner/designercore/include/nodeinstance.h

@@ -141,6 +141,8 @@ public:
 
     static void registerDeclarativeTypes();
 
+    QString id() const;
+
 #ifdef QTCREATOR_TEST
     QObject* testHandle() const;
     Internal::ObjectNodeInstance* internalInstance() const;

src/plugins/qmldesigner/designercore/instances/nodeinstance.cpp

@@ -644,6 +644,11 @@ void NodeInstance::registerDeclarativeTypes()
 //    qmlRegisterType<QmlDesigner::Internal::QmlPropertyChangesObject>();
 }
 
+QString NodeInstance::id() const
+{
+    return m_nodeInstance->id();
+}
+
 #ifdef QTCREATOR_TEST
 QObject* NodeInstance::testHandle() const
 {

src/plugins/qmldesigner/designercore/instances/nodeinstanceview.cpp

@@ -699,8 +699,8 @@ void NodeInstanceView::removeIdFromContext(QObject *object)
 {
     if (hasInstanceForObject(object)) {
         NodeInstance instance = instanceForObject(object);
-        if (instance.internalInstance()) {
-            QString id = instance.internalInstance()->id();
+        if (instance.isValid()) {
+            QString id = instance.id();
             if (!id.isEmpty())
                 engine()->rootContext()->setContextProperty(id, 0);
         }