fix(battery): Crash when `format-low` not defined
fix(battery): Crash when `format-low` not defined

This was a backwards-incompatible change introduced in #2199, however it
was caused because `module_formatter.has` throws an exception when the
format doesn't exist instead of just returning false.

Fixes #2262
Ref #2199

jaagr/polybar,jaagr/polybar,jaagr/polybar