Fix the PG listing issue which could miss objects for EC pool (where there is object shard and generation).
Backport: firefly
Signed-off-by: Guang Yang (yguang@yahoo-inc.com)
Merge pull request #2088 from guangyy/wip-8733

Fix the PG listing issue which could miss objects for EC pool

Reviewed-by: Samuel Just <sam.just@inktank.com>