Add null check to AbstractStateChangeTouchController#onDragEnd()

    @Override

    public void onDragEnd(float velocity) {

        if (mCurrentAnimation == null) {

            // Unlikely, but we may have been canceled just before onDragEnd(). We assume whoever

            // canceled us will handle a new state transition to clean up.

            return;

        }

        boolean fling = mDetector.isFling(velocity);

        boolean blockedFling = fling && mFlingBlockCheck.isBlocked();