dendrite -- Incorrect parsing of the event default power level in event auth

Dendrite team reports:

The power level parsing within gomatrixserverlib was failing to parse the “events_default”
key of the m.room.power_levels event, defaulting the event default power level to zero in all cases.
In rooms where the “events_default” power level had been changed, this could result in
events either being incorrectly authorised or rejected by Dendrite servers.