PG::choose_acting: filter CRUSH_ITEM_NONE out of have

Fixes: #7672
Signed-off-by: Samuel Just <sam.just@inktank.com>
Merge pull request #1418 from ceph/wip-7672

PG::choose_acting: filter CRUSH_ITEM_NONE out of have

Reviewed-by: Sage Weil <sage@inktank.com>