BUG #15060. Fixed issue when using TemporalShiftScale.

The problem was that when the current timesteps changed, we didn't snap
the current time to the new timesteps. That meant that we continued to
show the same old timestep even though the pipeline timesteps changed.
We fix this behavior by ensuring that we snap to a valid timestep when
the timesteps change and the animation is in "snap to timesteps" mode.

Change-Id: Ib6d1c1ca22eedf84cc8e9aa36592ad403d10a172
Merge topic '0015060_fix_temporalshift_issue' into next

4a3f3687 BUG #15060. Fixed issue when using TemporalShiftScale.