Bug: sending [stop( to [line~] when it's not running seems to jump the current value

[dromer]

Seeing this with some basic envelopes where the Release triggers a [stop( message and we hear volume jump instead of staying where it is.

Suspicion is this logic: o->x += o->m; from https://github.com/Wasted-Audio/hvcc/blob/develop/hvcc/generators/ir2c/static/HvSignalLine.c#L106-L138

Have tried with various test patches that showcase the issue: