Fix NPE when ripples are canceled due to visibility change

        final int count = mAnimatingRipplesCount;

        final Ripple[] ripples = mAnimatingRipples;

        for (int i = 0; i < count; i++) {

            ripples[i].cancel();

            // Calling cancel may remove the ripple from the animating ripple

            // array, so cache the reference before nulling it out.

            final Ripple ripple = ripples[i];

            ripples[i] = null;

            ripple.cancel();

        }

        mAnimatingRipplesCount = 0;