Bug: some animated png files are not tagged as animated

post #6999039
post #7563338

are not tagged as animated, and as animated png, and I can't tag them.

Tagging looping animation forces them to also be tagged animated but yes this is a bug.
(Still can't tag animated png)

issue #5709. Looks like FFmpeg can't handle these files, which means we don't detect them as animated, which means you can't add the animated png tag.