Prevent pointerIndex out of range IllegalArgumentException in ViewPager.

Recover from an inconsistent state where mActivePointerId no longer references a valid tracked pointer.
This may happen if a child view consumes part of the touch event stream, or is doing unsafe dispatching of touch events from #onInterceptTouchEvent.

Bug: 24191418
Change-Id: I1eda1d0ae435cf1b69918f521491c24b8f90203e
1 file changed