Correctly filter the weight unit
Correctly filter the weight unit

The previous code (based on an example on the metricsgraphics page) was built
on the premise that each day had an entry.

rolandgeider/wger,kjagoo/wger_stark,petervanderdoes/wger,wger-project/wger,DeveloperMal/wger,petervanderdoes/wger,rolandgeider/wger,DeveloperMal/wger,petervanderdoes/wger,rolandgeider/wger,DeveloperMal/wger,wger-project/wger,kjagoo/wger_stark,rolandgeider/wger,petervanderdoes/wger,kjagoo/wger_stark,DeveloperMal/wger,wger-project/wger,kjagoo/wger_stark,wger-project/wger