message: Fix potential error in File::get_file_pos
diff: @@ -598,7 +598,11 @@ uint64_t File::get_file_pos(FileDesc fd)
  return uint64_t(res.QuadPart);
  #else
  - return lseek(fd, 0, SEEK_CUR);
  + auto pos = lseek(fd, 0, SEEK_CUR);
  + if (pos < 0) {
  + throw std::system_error(errno, std::system_category(), "lseek() failed");
  + }
  + return uint64_t(pos);
  #endif
  }
  