message: Fix crash: only traverse graph to add existing symbols if symbol table presents
diff: @@ -428,7 +428,9 @@ class ShapeInferenceImplBase {
  }
  void process(GraphProto& graph) {
  + if (symbol_table) {
  TraverseGraphsToAddExistingSymbols(graph, *symbol_table);
  + }
  for (auto& vi : *graph.mutable_value_info()) {
  updateType(vi);
  }
  