message: Forbid possible ir_version=0 in IR
diff: @@ -374,7 +374,8 @@ std::unique_ptr<Graph> graphProtoToGraph(const ONNX_NAMESPACE::GraphProto& gp, b
  std::unique_ptr<Graph> ImportModelProto(const ModelProto& mp) {
  if (!mp.has_ir_version()) {
  return nullptr;
  - } else if (mp.ir_version() == 1) {
  + } else if (mp.ir_version() <= 1) {
  + // ir_version=1 is not supported and ir_version=0 is illegal
  return nullptr;
  }
  