Avoid multiple indexing of edges

bnb/graph.cpp

@@ -4,6 +4,7 @@ graph::graph(std::vector<std::vector<unsigned int>> a) : nodes_(a.size()), adjac
 }
 
 void graph::index_edges() {
+    if (!indexed_edges_.empty()) return;
 	edge_id eid = 0;
 	
 	for (node_id u = 1; u <= nodes_; u++) {