bug#57691: 29.0.50; image-tests failures

[Stefan Kangas]

Eli Zaretskii <eliz@gnu.org> writes:

>> This looks like some version of librsvg giving a different error
>> message.  Does the attached patch fix this for you?
>
> Yes, thanks.
>
>> Also, out of interest, do you know which version of librsvg you're
>> using?
>
> 2.40.1.

Mine is 2.50.3, so I guess the message format has changed.  The fix is
pushed to master, thanks for testing.