fix typo on bad member access

graph.cpp

@@ -200,8 +200,8 @@ void Graph::reset_forest()
 {
    NodeId cur_id = 0;
    for(auto & node : _nodes) {
-      node._ear_or_root_neighbor = cur_id;
-      node._root_of_ear_component = cur_id;
+      node.ear_or_root_neighbor = cur_id;
+      node.root_of_ear_component = cur_id;
       // Note that we do not change the matching itself here
    }
 }