During startup, InnoDB must write a FILE_CHECKPOINT record.
However, before MDEV-12353 (in MariaDB Server 10.2, 10.3, 10.4)
the corresponding record MLOG_CHECKPOINT was encoded in a different way.

When we are upgrading from a logically empty 10.2, 10.3, or 10.4 redo log,
we must not write anything to the old log file, because if the server were
killed during the upgrade, we would end up with a corrupted log file, and
both the old and the new server would refuse to start up.

On upgrade, we must simply create a new logically empty log file
and replace the old ib_logfile0 with that.