added missing type registration

source/ArmarXGui/gui-plugins/StatechartViewerPlugin/layout/LayoutWorkerCreator.cpp

@@ -35,6 +35,8 @@ armarx::LayoutWorkerCreator::LayoutWorkerCreator()
     //    aginit();
     ARMARX_INFO_S << "Graphviz initialized";
     qRegisterMetaType<MediatorPtr>("MediatorPtr");
+    qRegisterMetaType<LockableGraphPtr>("LockableGraphPtr");
+
     graphvizContext = gvContext();
 }