bug#56469: 29.0.50; Unibyte dir in directory_files_internal

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: 56469@debbugs.gnu.org
> Date: Sun, 10 Jul 2022 18:13:39 -0400
> 
> > I don't think file-name related stuff can work in Emacs when
> > file-name-coding-system is set to an arbitrary value not reflecting
> > the reality.
> 
> I'd tend to agree (tho 'binary' does sound like a valid value which
> should work in all cases under GNU/Linux).

'binary' exactly means that you end up with unibyte strings and with
raw bytes in multibyte strings.

> I'm just a bit annoyed at the idea that ELisp code can end up
> constructing a multibyte string whose bytes contain invalid utf-8
> sequences, because I suspect we may end up with a core dump somewhere in
> such a circumstance.

Emacs should cope with this without dumping core, but the resulting
file names might not be readable by humans nor friendly to other
programs.