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

[Eli Zaretskii]

> From: Andy Moreton <andrewjmoreton@gmail.com>
> Date: Sat, 14 Oct 2017 19:16:11 +0100
> 
> > I see no problems with those images you mention as problematic.
> >
> > Could it be a problem specific to 64-bit builds?
> 
> I've tried this in a 32bit MinGW build with the same results. It appears
> to be a problem with the pbm entry in image-type-header-regexps, as
> doing (setq image-type-header-regexps '(("\\`P[1-6]" . pbm))) results in
> the problematic images displaying correctly.

Then why does it work here with the unmodified PBM entry?