Allow finding the "original remote thumbnail"
Allow finding the "original remote thumbnail"

This will probably cause older oEmbed images not to show, since they
probably were updated to use empty url entries because they were thought
of as local ones. During a migration period maybe you want to change
the default value of notNullUrl to 'false' in File_thumbnail::byFile(...)

charnimda/lgbtpzn-social,charnimda/lgbtpzn-social,foocorp/gnu-social,foocorp/gnu-social,charnimda/lgbtpzn-social,foocorp/gnu-social,chimo/social,chimo/social,chimo/social