rm: --dir (-d): fix bugs in handling of empty, inaccessible directories

rm: --dir (-d): fix bugs in handling of empty, inaccessible directories

* src/remove.c (prompt, rm_fts): In the dir-handling code of both of
these functions, relax a "get_dir_status (...) == DS_EMPTY" condition
to instead test only "get_dir_status (...) != 0", enabling flow control
to reach the prompt function also for unreadable directories. However,
that function itself also needed special handling for this case:
(prompt): Handle empty, inaccessible directories properly,
deleting them with -d (--dir), and prompting about whether to delete
with -i (--interactive).
* tests/rm/empty-inacc.sh: Add tests for the new code.
Reported by наб <nabijaczleweli@nabijaczleweli.xyz> in
bugs.debian.org/1015273
* NEWS (Bug fixes): Mention this.