::automation_run() evaluates the value, possibly ahead of time
depending on latency-compensation. The actual value is set in
realtime-context via set_value_unchecked() -> actually_set_value()
which emits the Changed signal.
At this point in time Control::user_value is already set correctly.
There is no need to evaluate and interpolate again, at a potentially
incorrect (uncompensated) time: `_session.transport_sample()`.
This fixes an issue with the GUI Automation control showing an
outdated value when there is an "immediate jump" in the signal:
eg. add a latent plugin post-fader, then automate the Fader to jump
from 0dB to -inf dB (snap to grid) and play though that transition.
(Plugin controls were not affected by this bug, the process
cycle is split for those, but Mixbus internal AC were affected).
5cb6e1046b