Fix: Group Nodes operator fails to mark new group as updating

ops_nodegroup.py

@@ -86,7 +86,11 @@ class MantisGroupNodes(Operator):
 
             grp_node.location = Vector((all_nodes_bounding_box[0].x+200, all_nodes_bounding_box[0].lerp(all_nodes_bounding_box[1], 0.5).y))
             from .base_definitions import node_group_update
-            node_group_update(grp_node, force=True)
+            grp_node.is_updating=True
+            try:
+                node_group_update(grp_node, force=True)
+            finally:
+                grp_node.is_updating=False
 
             # for each node in the JSON
             for n in selected_nodes[base_tree.name][2].values():