AniList refiner: Gracefully handle missing anilist_id attribute

[ThisIsntTheWay]

This change prevents the refiner from throwing an error in situations where matched entries in the reference list don't have an anilist_id attribute, as it is the case with this entry (at time of writing):

> $list | ? imdb_id -eq "tt3138698"

thetvdb_id    : 102261
imdb_id       : tt3138698
anisearch_id  : 6334
themoviedb_id : 357786
anidb_id      : 8357
type          : MOVIE