Avoid potential infinite recursion when building a descriptor

check_whether_dirport_reachable(void)

{

  or_options_t *options = get_options();

  routerinfo_t *ri = router_get_my_routerinfo();

  return !options->DirPort ||

         options->AssumeReachable ||

         (ri && !ri->dir_port) ||

         we_are_hibernating() ||

         can_reach_dir_port;

}