Fix map read / write panic in aggmetrics
Fix map read / write panic in aggmetrics

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