[Bug] Backend filter expression doesn't work with single element in IN condition

[yesoreyeram]

Bug report copied from the community.grafana.com

With backend filter expression, The filter works fine when we set multiple options where as fails when we set with single option instead of Multiple option.

More about this https://community.grafana.com/t/from-csv-how-to-filter-multiple-values-using-infinity-data-source/116580/12

underlying issue : Knetic/govaluate#79

[shuiqingliu]

same issue