fix(previews): Don't crash on animated WEBP images

fix(previews): Don't crash on animated WEBP images

Fixes #30029 and #37263

libgd handles animated WEBP images poorly and generates a meaningless error message as a result. We were returning a 500 error for these preview requests (web) and a fatal error at the command-line (occ). Now we bypass libgd if the we detect an animated WEBP image (and simply don't generate the preview). No more 500 error. Should fix occ too.

Signed-off-by: Josh Richards <josh.t.richards@gmail.com>
Signed-off-by: Richard Steinmetz <richard@steinmetz.cloud>