bug#28824: 26.0.90; display of pbm images broken?

[Eli Zaretskii]

> From: Andy Moreton <andrewjmoreton@gmail.com>
> Date: Sat, 14 Oct 2017 20:03:27 +0100
> 
> Further testing with the images from etc/images in emacs 26 shows that
> this patch appears to fix the problem:
> 
> diff --git a/lisp/image.el b/lisp/image.el
> index 1d0776180b..32df508bc8 100644
> --- a/lisp/image.el
> +++ b/lisp/image.el
> @@ -34,8 +34,8 @@ 'image-refresh
>  (defconst image-type-header-regexps
>    `(("\\`/[\t\n\r ]*\\*.*XPM.\\*/" . xpm)
>      ("\\`P[1-6]\\(?:\
> -\\(?:\\(?:#[^\r\n]*[\r\n]\\)?[[:space:]]\\)+\
> -\\(?:\\(?:#[^\r\n]*[\r\n]\\)?[0-9]\\)+\
> +\\(?:\\(?:#[^\r\n]*[\r\n]\\)*[[:space:]]\\)+\
> +\\(?:\\(?:#[^\r\n]*[\r\n]\\)*[0-9]\\)+\
>  \\)\\{2\\}" . pbm)
>      ("\\`GIF8[79]a" . gif)
>      ("\\`\x89PNG\r\n\x1a\n" . png)

Thanks.  However, I'm puzzled by the fact that it works here without
any changes.

Can you step with a debugger through the code in image.c and tell what
exactly fails with the unmodified regexp?