Fix possibility of ScrollView not allowing clicks after a fling

The reason that manifests is because SV's
onInterceptTouchEvent checks if it's scroller.isFinished()
returns true. The result of Scroller.isFinished() is only
valid if it has had computeScrollOffset() called on it before.

ScrollView currently posts a invalidation after a computeScroll()
call, which means that isFinished() *should* be valid, but it's
better to be explicit which CL adds.

BUG: 26051101
Change-Id: If78f48dc855de1776011cb7b0f95cb0a80d9b777