Playtime: Enabling/disabling FX with PDC during REAPER playback totally destroys timing

[helgoboss]

The following issue can be observed when having latency-heavy FX on the master FX chain. It's PDC-related.

Can easily be tested by putting ReaFir on the master track with a huge FFT size (e.g. 32768).

Enabling/disabling such FX while REAPER is playing, retriggers clips

This should ideally be fixed by using a form of resyncing (by tracking a hypothetical playback position).

Reported by jimmydeluxe: https://www.youtube.com/watch?v=EhjGHFEyW3I

For the case that REAPER transport is stopped, this has already been solved in #1164.

[helgoboss]

When fixing this with Justin's addition, I should also check if leftward smooth-seek and looping works with high-latency FX.