Bugfix: support unknown control op subgraph

tests/ut/ge/hybrid/ge_hybrid_unittest.cc

@@ -289,8 +289,10 @@ TEST_F(UtestGeHybrid, unfold_subgraphs_success) {
   partitioned_call_node->GetOpDesc()->AddSubgraphName("sub_graph");
   partitioned_call_node->GetOpDesc()->SetSubgraphInstanceName(0, "sub_graph");
 
-  sub_sub_graph1->AddSubGraph(sub_sub_graph1);
-  sub_sub_graph2->AddSubGraph(sub_sub_graph2);
+  root_graph->AddSubGraph(sub_sub_graph1);
+  root_graph->AddSubGraph(sub_sub_graph2);
+  sub_sub_graph1->SetParentGraph(root_graph);
+  sub_sub_graph2->SetParentGraph(root_graph);
 
   root_graph->AddSubGraph(sub_graph);
   sub_graph->SetParentNode(partitioned_call_node);