fts: nlink_t signedness fixups * lib/fts.c (fts_open): Set rootparent n_dirs_remaining to -1 so that root need not be a special case later. (fts_read): Remove now-redundant test for fts_level. Do not assume that nlink_t is signed. (fts_build): Remove useless decrement of nlinks. (fts_stat): Avoid unlikely signed integer overflow later, if nlink_t is signed.