Amperage reads zero when voltage supply not connected

[David00]

This is an issue discovered in the v0.3.0 release that reports 0 amps on a sensor when the following two conditions are met:

• The watts_cutoff_threshold is set to something other than 0 in config.toml
• The 9V AC supply is not connected (or not supplying grid voltage) to the PCB

I've already fixed the issue and will push a commit that addresses this issue shortly.