No signal offset in Fast Mode (PID-only Mode)

[bleykauf]

          I observed another issue with the fast mode settings. 

Using Linien 0.7.0.

Here is the signal I am trying to lock:

I am setting a signal offset and using a manual lock.

With fast mode disabled:

With fast mode enabled:

It's as if the signal offset value is getting set to 0, preventing the integrator from changing signs

Originally posted by @andrewvh4 in #314 (comment)