Fix Dired display of an explicit list of files by ls-lisp.el

Fix Dired display of an explicit list of files by ls-lisp.el

* lisp/ls-lisp.el (ls-lisp-uid-d-fmt, ls-lisp-uid-s-fmt)
(ls-lisp-gid-d-fmt, ls-lisp-gid-s-fmt): Make the initial values be
correct for when displaying individual files separately, not as
part of listing a directory, in which case these values are not
recomputed by 'ls-lisp-insert-directory', but used verbatim.