EDA - lineplot empty but the back end data looks good

[bobular]

I was checking up on any front end issues related to #762 and VEuPathDB/plot.data#253 and found a nasty bug on both production site and dev sites (https://dfalke-b.clinepidb.org) - so this is nothing to do with the change in binning behaviour as far as I can tell

Reproduce

• GEMS1
• no filters
• line plot
• x = study year
• y = water trips per week

Outcome is an empty plot but the data from the back end looks good

Data from NEW back end on dev

Data from OLD back end on production

[bobular]

For info:
Study year is
type = integer
dataShape = ordinal
vocabulary = [ "1", "2", "3" ]