BUG: tracks without audio features causes problems with the Spotify.Track.audio_features function

[Pineapple217]

The Spotify.Track.audio_features function returns nil instead of an error.
An error occurs because there is a track without audio features. This is not intended as far as I know and an error on Spotify's side but it does exist. 1OegbevPjnz3BBlyzkBT4K this is an id of a track that has no audio features.

It would be nice if the function would return :error. The nil return also means that if you query lost of IDs that you cant get the info of the tracks that didn't fail.