Fix misc. bugs in AbsListView smooth scrolling.

Handle the edge cases a bit better. Deal with padding. If a smooth
scroll begins, the list is empty, but a data change is pending, try
again on the next looper pass.

Bug 6453837
Bug 6434713

Change-Id: I53f22ebacdcbc5d981a6c8055c4fd3fc1ef140f6