osd/PeeringState: recover_got - add special handler for empty log

osd/PeeringState: recover_got - add special handler for empty log

If we use a small osd_min[max]_pg_log_entries setting, say, 10, and
do splitting, a child pg may only be able to keep some divergent log
entries in the list. Any follow-up peering cycle on that child pg
would then rewind all the divergent log entries and lead to an empty
log list, which as a result could reliably fire the

  ceph_assert(info.last_complete == info.last_update)

assert if we start to recover any of the missing divergent objects
later.

Fixes: https://tracker.ceph.com/issues/41816
Signed-off-by: xie xingguo <xie.xingguo@zte.com.cn>
(cherry picked from commit a5e9e9099865be7a3d90c58cf3f3fc50ed6eed6d)

Conflicts:
	src/osd/PeeringState.cc
- file does not exist in the stable branch: made the changes manually to
  src/osd/PrimaryLogPG.cc