Make fields in UserPlayingNowListen optional

[rotmoded]

when attempting to fetch playingnows from the listenbrainz api, i kept running into errors like Json(Error("missing field inserted_at" because the api wasn't providing those fields at the endpoint for the listens list. i made them optional and it no longer panics.

[InputUsername]

Thanks for reporting this! It actually looks like ListenBrainz silently changed some of their response schemas :frowning_face:

I'm going to close this one and address your issue together with the other problems in #13. Thanks again for bringing this to light.