osd: PGLog Attach correct version to missing list when ignoring log entries

A previous fix for PR 66698 fixed an issue where log entries associated with
partial writes were being processed incorrectly (see that PR and associated
tracker for details).  The fix was to ignore log entries that should not have
been present on the non-primary shard.

The problem with that approach is that in a more complex scenario, where the
log contained a partial write, followed by a full write AND the shard is
backfilling, then the missing list was being given the version prior to the
full write, rather than prior to the clone.

Our fix here corrects how the missing list version is calculated.

See the associated tracker for instructions on how to recreate

Fixes: https://tracker.ceph.com/issues/75211
Signed-off-by: Alex Ainscow <aainscow@uk.ibm.com>