ReplicatedPG::wait_for_degraded_object: only recover if found

Fixes: #7618
Signed-off-by: Samuel Just <sam.just@inktank.com>
Merge pull request #1387 from ceph/wip-7618

ReplicatedPG::wait_for_degraded_object: only recover if found

Reviewed-by: Sage Weil <sage@inktank.com>