bug#51296: [PATCH] Add WebP format support

[Stefan Kangas]

Eli Zaretskii <eliz@gnu.org> writes:

> And if you use SDATA instead of SSDATA?

Yes, that fixed it.  I guess SSDATA is there specifically to avoid
casting warnings, but in this case only produced one...

> Otherwise, I think this is good to go, thanks.

Great!  If it's fine by you, I will push this to master tomorrow (or the
day after) at a time when you are typically online, just in case there
is any fallout on MS-Windows.