Avoid excluding guards from path building in minimal test networks

  o Minor bugfixes:

    - Avoid excluding guards from path building in minimal test networks,

      when we're in a test network, and excluding guards would exclude

      all nodes. This typically occurs in incredibly small tor networks,

      and those using TestingAuthVoteGuard *

      This fix only applies to minimal, testing tor networks,

      so it's no less secure.

      Discovered as part of #13718.

        smartlist_add(excluded, (void*)node);

    });

  }

  /* and exclude current entry guards and their families, if applicable */

  /* and exclude current entry guards and their families,

   * unless we're in a test network, and excluding guards

   * would exclude all nodes (i.e. we're in an incredibly small tor network,

   * or we're using TestingAuthVoteGuard *).

   * This is an incomplete fix, but is no worse than the previous behaviour,

   * and only applies to minimal, testing tor networks

   * (so it's no less secure) */

  /*XXXX025 use the using_as_guard flag to accomplish this.*/

  if (options->UseEntryGuards) {

  if (options->UseEntryGuards

      && (!options->TestingTorNetwork ||

          smartlist_len(nodelist_get_list()) > smartlist_len(get_entry_guards())

     )) {

    SMARTLIST_FOREACH(get_entry_guards(), const entry_guard_t *, entry,

      {

        if ((node = node_get_by_id(entry->identity))) {