Fail-fast if thumbnailing PDF fails.
Fail-fast if thumbnailing PDF fails.

I've attempted to regenerate all the attachment thumbnails in
production. By failing fast like this, we should get some more clues as
to why some thumbnailing may still be failing.

YOTOV-LIMITED/whitehall,hotvulcan/whitehall,ggoral/whitehall,YOTOV-LIMITED/whitehall,ggoral/whitehall,robinwhittleton/whitehall,YOTOV-LIMITED/whitehall,YOTOV-LIMITED/whitehall,robinwhittleton/whitehall,askl56/whitehall,alphagov/whitehall,askl56/whitehall,ggoral/whitehall,hotvulcan/whitehall,askl56/whitehall,askl56/whitehall,hotvulcan/whitehall,robinwhittleton/whitehall,alphagov/whitehall,ggoral/whitehall,alphagov/whitehall,robinwhittleton/whitehall,alphagov/whitehall,hotvulcan/whitehall