bug#18632: 24.3.94; image-dired fail when `image-dired-dir' doesn't exist

[Eli Zaretskii]

> From: Stefan Kangas <stefan@marxist.se>
> Date: Fri, 30 Aug 2019 00:32:52 +0200
> Cc: 18632@debbugs.gnu.org
> 
> I can reproduce this on current master.  The problem happens when the
> user removes the image-dired-dir directory (normally
> ~/.emacs.d/image-dired).
> 
> Steps to reproduce:
> 
> 0. emacs -Q
> 1. C-x C-f ~/my-image-dir
> 2. (in shell) rm -rf ~/.emacs.d/image-dired/  # value of (image-dired-dir)
> 3. (in emacs): RET
> 
> Now I see the error message "Unable to resize".

How about recreating the missing directory in this case, after asking
for user's permission?