remove needless check
remove needless check

it's needless because before these calls, we already confirmed
len(Chunks) > 0 and made sure the index is valid.

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