[Serious] Setting Cable Resistance Factor to 0

[OmegaHaxors]

It's possible to set the Cable Resistance Factor to 0, and doing so causes singular networks (those with no resistance but a source and a sink) to produce NaN networks.

Simple fix is to make Ground cables exempt from the config so that Singular Matrices are no longer possible, since all other power sources and sinks have at least a tiny bit of resistance.

EDIT: I was wrong. Machines can also cause NaN errors. It's probably due to the config also changing resistance values on non-cable blocks. This is really not acceptable, and should be sorted out quickly.

[Baughn]

A better fix is to make it impossible to set resistance to 0.