doesn't recover once basebackup_delta_mode_max is reached

# What happened?

taking base backups failed for quite a long time (many hours), resulting in the retry count for the backup site to be reached.

even once the circumstances changed (likely allowing backups again), base backups aren't resumed.

# What did you expect to happen?

I'd expect rate-limiting of the number of retries (as happened), but that attempts to take a base backup still continue.