Fixed weirdness about last icon in shelf

The last icon in shelf could jump around and behave
Erratically because of an optimization around it's
transformation.
If the maxShelfEnd changed non-continuously, for example
With an expansion, the icon would jump-cut.

Test: add a few notifications, while no shelf available, expand notification
Before the last one, observe no jump-cut

Change-Id: I4b05f340cb1715f7bf80f5e96582a56a6f62ce1b