QmlDesigner: avoid crash

There can be notifications from the instance
after a model node has been deleted.
We now ignore those.

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

@@ -79,7 +79,7 @@ int NodeInstanceSignalSpy::qt_metacall(QMetaObject::Call call, int methodId, voi
     if (call == QMetaObject::InvokeMetaMethod && methodId > QObject::staticMetaObject.methodCount()) {
         ObjectNodeInstance::Pointer nodeInstance = m_objectNodeInstance.toStrongRef();
 
-        if (nodeInstance && nodeInstance->nodeInstanceView()) {
+        if (nodeInstance && nodeInstance->nodeInstanceView() && nodeInstance->modelNode().isValid()) {
             nodeInstance->nodeInstanceView()->notifyPropertyChange(nodeInstance->modelNode(), m_indexPropertyHash.value(methodId));
         }
 

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

@@ -568,6 +568,8 @@ void NodeInstanceView::notifyPropertyChange(const ModelNode &node, const QString
 {
     if (m_blockStatePropertyChanges)
         return;
+    if (!node.isValid())
+        return;
 
     emitInstancePropertyChange(QList<QPair<ModelNode, QString> >() << qMakePair(node, propertyName));
 }