Consistent exclusion of subgraph inputs when traversing nodes. (#3171)

src/ngraph/graph_util.cpp

@@ -74,9 +74,12 @@ void ngraph::traverse_nodes(const NodeVector& subgraph_results,
     std::deque<std::shared_ptr<Node>> stack;
 
     for (auto r : subgraph_results)
+    {
+        if (instances_seen.count(r) == 0)
         {
             stack.push_front(r);
         }
+    }
 
     while (stack.size() > 0)
     {