bug#20739: 25.0.50; Dired switches have no effect when explicit list of files provided

[Drew Adams]

> a bug for `B':
...
> Debugger entered--Lisp error: (file-error "Opening directory"
>  "No such file or directory" "d:/the/path/to/foo.el/foo.el/")
>   directory-files-and-attributes("foo.el/" nil "[^~]\\'" t string)
>   ls-lisp-insert-directory("foo.el" (66) nil "[^~]\\'" nil)
>   ls-lisp--insert-directory(...

FYI, I submitted the fix as a patch in a separate bug report, #20776.