Fix #140381: Crash after deleting a node group and redo

The fix in #140381 addressed the crash after redo. This commit fixes
the crash after redo (make group) and deleting the node group.

Pull Request: https://projects.blender.org/blender/blender/pulls/140858

source/blender/editors/space_node/node_edit.cc

@@ -2091,6 +2091,7 @@ static wmOperatorStatus node_delete_exec(bContext *C, wmOperator * /*op*/)
     }
   }
 
+  ED_node_set_active_viewer_key(snode);
   BKE_main_ensure_invariants(*bmain, snode->edittree->id);
 
   return OPERATOR_FINISHED;