fix return when backfill done
fix return when backfill done

raintank/metrictank,replay/metrictank,replay/metrictank,replay/metrictank,replay/metrictank,raintank/metrictank,raintank/raintank-metric,raintank/raintank-metric,raintank/raintank-metric,raintank/metrictank,raintank/metrictank