message: fix error on GRPC Python - ignore namespace tree if not specified
diff: @@ -403,8 +403,10 @@ bool GeneratePythonGRPC(const Parser &parser, const std::string & /*path*/,
  namespace_dir += *it;
  }
  - std::string grpc_py_filename =
  - namespace_dir + kPathSeparator + file_name + "_grpc_fb.py";
  + std::string grpc_py_filename = namespace_dir;
  + if (!namespace_dir.empty()) grpc_py_filename += kPathSeparator;
  + grpc_py_filename += file_name + "_grpc_fb.py";
  +
  return flatbuffers::SaveFile(grpc_py_filename.c_str(), code, false);
  }
  