Time Series Request always returns a min of 0

[Tomcariello]

When making a time series request, the min value for each step of the returned object is 0.

https://d1igaxm6d8pbn2.cloudfront.net/get_stats?_type=series&timestamp=2020-03-15&steps=10&layer=OMI_Aerosol_Index&colormap=OMI_Aerosol_Index.xml&bbox=-6.827411984774017,-216.16109095833258,49.42258801522598,-98.03609095833258&bins=10&end_timestamp=2021-03-08

min: { ,"2020-03-15T00:00:00Z": 0, "2020-04-19T00:00:00Z": 0, "2020-05-24T00:00:00Z": 0, "2020-06-28T00:00:00Z": 0, "2020-08-02T00:00:00Z": 0, "2020-09-06T00:00:00Z": 0, "2020-10-11T00:00:00Z": 0, "2020-11-15T00:00:00Z": 0, "2020-12-20T00:00:00Z": 0, "2021-01-24T00:00:00Z": 0, "2021-02-28T00:00:00Z": 0, }

And another request: https://d1igaxm6d8pbn2.cloudfront.net/get_stats?_type=series&timestamp=2018-03-15&steps=10&layer=AIRS_L2_Carbon_Monoxide_500hPa_Volume_Mixing_Ratio_Day&colormap=AIRS_Carbon_Monoxide_Volume_Mixing_Ratio.xml&bbox=-4.858661984774017,23.46390904166742,28.891338015225983,41.46390904166742&bins=10&end_timestamp=2019-03-08

min: { "2018-03-15T00:00:00Z": 0, "2018-04-19T00:00:00Z": 0, "2018-05-24T00:00:00Z": 0, "2018-06-28T00:00:00Z": 0, "2018-08-02T00:00:00Z": 0, "2018-09-06T00:00:00Z": 0, "2018-10-11T00:00:00Z": 0, "2018-11-15T00:00:00Z": 0, "2018-12-20T00:00:00Z": 0, "2019-01-24T00:00:00Z": 0, "2019-02-28T00:00:00Z": 0 }

[frankinspace]

I'm suspecting this is the problem:

https://github.com/podaac/gibs-imagestat/blob/develop/imagestat/api.py#L125