should fix #2320

Sources::Site#normalize_for_artist_finder! catches errors that occur
during the normalization process. However it only catches
StandardErrors, not Exceptions, so this makes Sources::Error a
StandardError.
Don't make pixiv http requests when displaying artist history

The reason the urls need to be normalized at all here is because legacy
urls from Danbooru 1 don't have their unnormalized counterparts stored
anywhere and thus can't be accurately compared with unnormalized urls
from Danbooru 2.