NumberPicker getting stuck if scroll wheel not wrapable.

1. If the number picker was not wrapping the selector wheel
   it was incorrectly initializing the fling scroller and
   the error was proportional to the difference of the
   current value and the max size. As a result if the number
   picker gets stuck for a very long time.

2. The alpha of the selector wheel paint was not reset on
   every subsequent fling so if the wheel was fading out
   and a new fling is performed the selector wheel is
   dimmed during the fling, rather bright.

bug:5728363

Change-Id: Ia90a6af86f162bda1b28f43f7ba7e4a9f5051b78