osd: Divergent logs for pure partial writes should roll back mising list when merged.

osd: Divergent logs for pure partial writes should roll back mising list when merged.

When a log was applied for a partial write to an object that is async recovering, the
log will be rolled forward and the missing list updated.

If this log becomes divergent, then we must rollback the update to the missing list
in the merge.

Fixes: https://tracker.ceph.com/issues/75962
Signed-off-by: Alex Ainscow <aainscow@uk.ibm.com>