The new carousel implementation was lacking some scroll related
behaviours. This makes sure that post-filter, the selection is
re-centered *unless* the user has scrolled away manually.
This matches the old carousel's behaviour. See
https://github.com/ppy/osu/pull/16647 for original implementation.
Closes https://github.com/ppy/osu/issues/33052.
Pushing this out with zero testing as a "probably fixes"
https://github.com/ppy/osu/issues/33108.
Previous logic would mean that the start value of the fade-in may not be
zero depending on current state, leaving the final alpha state incorrect
after a rewind beyond the start time.