bug#56182: 28.1; Display of SVG file with transparent background is incorrect

[Eli Zaretskii <eliz@gnu.org>]

> From: Corwin Brust <corwin@bru.st>
> Date: Tue, 12 Sep 2023 08:55:37 -0500
> 
> Compile: yes.  Fixes the problem: unsure.
> 
> I did not have difficulty building the emacs-29 branch with this patch
> applied. Unfortunately, I could not confirm (or disprove) the success
> of the patch because I received (under -Q) "Invalid Image
> Specification" trying to load etc/images/down.svg.  Here's a
> screenshot:
> 
> https://bru.st/i/emacs-29.1.50.1_i9DY4oaggq.png
> 
> I then confirmed I get this same from a recent (upatched:
> ca95e45f7e828aebdf2736c9c7b2d64f9621214e) build from the development
> branch.  Others I grabbed at random also give this error now, so I'm
> confident it's nothing to do with down.svg.  An unpatched emacs-28
> build could display SVGs, I remember that 29.1 can but didn't check.
> Is it possible there's a recent regression breaking SVG image display
> more generally (perhaps merged up, already)?

I see no problems with SVG images here, but my librsvg is quite old,
so maybe the regression happened in parts that are not compiled with
my librsvg.

> Should I open a seperate bug report?

Yes, please.

Thanks.