Non-expiring polls (ie. MissKey) show "poll ends in 50y"

When expires_at in the MastoAPI Poll entity is null it wrongly shows "poll ends in 50y".

Link to the poll: https://misskey.io/notes/8chigu6kjd

How do we know Pleroma hasn't calculated the end of humanity to be ~50y?

The end of humanity will be in 1970-01-01 :DD

added Better behavior Bug labels

mentioned in merge request !1889 (merged)

mentioned in commit 23edfe7b

closed with merge request !1889 (merged)