Avoiding weird icon positions

When expanding quickly we switch to a linear interpolation.
In this case the last icon may be stuck in between the
shelf position and the notification position, which looks pretty bad.
We therefore optimize this case better to avoid these weird
in-between cases.

Test: manual, expand with various notifications
Fixes: 63088105
Fixes: 62374617
Change-Id: I95f72c9defc6c941a5a6a71829d239529c3861e9