Fix min/max calculation for empty series
Fix min/max calculation for empty series

The defaulting of min/max to 0 wasn't being applied in all
circumstances; if there were no datapoints at all, they would remain at
`Number.MAX_VALUE` and `Number.MIN_VALUE` respectively.

I'm not convinced this fully resolves the issues here (e.g. shouldn't it
be perfectly possible for sum to be 0 _and_ for min/max to have real
values, if you have a dataset of mixed negative/positive values or just
all zeros?), but it fixes my issue at least!

urbanairship/tessera,jmptrader/tessera,tessera-metrics/tessera,tessera-metrics/tessera,Slach/tessera,jmptrader/tessera,jmptrader/tessera,section-io/tessera,section-io/tessera,Slach/tessera,section-io/tessera,aalpern/tessera,Slach/tessera,aalpern/tessera,urbanairship/tessera,aalpern/tessera,jmptrader/tessera,tessera-metrics/tessera,urbanairship/tessera,urbanairship/tessera,aalpern/tessera,jmptrader/tessera,tessera-metrics/tessera,tessera-metrics/tessera,urbanairship/tessera,aalpern/tessera,Slach/tessera,section-io/tessera