Fix crash when node flags updated after delete node (#501)

Author: zekexiao

src/NodeGraphicsObject.cpp

@@ -60,7 +60,7 @@ NodeGraphicsObject::NodeGraphicsObject(BasicGraphicsScene &scene, NodeId nodeId)
 
     setPos(pos);
 
-    connect(&_graphModel, &AbstractGraphModel::nodeFlagsUpdated, [this](NodeId const nodeId) {
+    connect(&_graphModel, &AbstractGraphModel::nodeFlagsUpdated, this, [this](NodeId const nodeId) {
         if (_nodeId == nodeId)
             setLockedState();
     });