bug#61639: 30.0.50; [PATCH] Do not error out on non image file in image-dired

[Eli Zaretskii]

> From: Manuel Giraud <manuel@ledu-giraud.fr>
> Cc: 61639@debbugs.gnu.org
> Date: Tue, 21 Feb 2023 13:16:04 +0100
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> [...]
> 
> > Thanks.  This LGTM, but what is 'plusp'?
> 
> 'plusp' is a classic Common Lisp predicate (that also seems to be
> defined in Emacs).  It is equivalent to (> x 0)… maybe you prefer that.
> Should I fix my patch?

Where is it defined?  It isn't defined in "emacs -Q", and not after
loading image-dired.  (Tested in Emacs 29.)