osd: avoid ceph_abort in build_incremental_map_msg when newest_map is missing

osd: avoid ceph_abort in build_incremental_map_msg when newest_map is missing

When sharing OSD maps with a peer (e.g. during heartbeat in
maybe_share_map), we may have already trimmed the requested range or
newest_map (e.g. trim race, or store read failure). In that case the
panic path tried to send newest_map; if it could not be loaded, the
code called ceph_abort() and crashed the OSD.

Log and return an empty MOSDMap instead of aborting. The receiver drops
such messages (last <= superblock.get_newest_map()) and can re-request
from the mon.

Fixes: https://tracker.ceph.com/issues/74800
Signed-off-by: Vinayak Tiwari <tiwarivinayak10@gmail.com>