bug#50560: 28.0.50; 'insert-file-contents-literally' on multibyte buffers

[Eli Zaretskii]

> From: Augusto Stoffel <arstoffel@gmail.com>
> Cc: 50560@debbugs.gnu.org
> Date: Mon, 13 Sep 2021 14:44:24 +0200
> 
> > It is only essential for some very specific uses of the resulting
> > buffer, but definitely not for all.
> 
> That's a good point.  Maybe the issue is actually with 'create-image',
> which seems to only work correctly when the data is passed as a unibyte
> string, but gives no warning if you pass a multibyte one.

Maybe we should have create-image convert the :data string to unibyte
if it isn't already so.