osdc/Objecter: e shouldn't be zero in Objecter::handle_osd_map

Signed-off-by: Ding Dinghua <dingdinghua85@gmail.com>
osdc/Objecter: Fix a bug of dead looping in Objecter::handle_osd_map

If current map epoch is less than oldest epoch, current map epoch
should step up to oldest epoch.

Fixes: #9986
Signed-off-by: Ding Dinghua <dingdinghua85@gmail.com>
Merge pull request #2851 from ceph/wip-9986

objecter: fix map skipping

Reviewed-by: Sage Weil <sage@redhat.com>