CacheableBitmapDrawable sets null in detach, should probably just set unused

[arberg]

I suggest to replace current onDetachFromWindow with

@Override
protected void onAttachedToWindow() {
    super.onAttachedToWindow();
    onDrawableUnset(getDrawable());
}

@Override
protected void onDetachedFromWindow() {
    super.onDetachedFromWindow();
    onDrawableSet(getDrawable());
}

I had an issue earlier which caused me to disable using CacheableBitmapDrawable in favor of ImageView. I have now tested again with CacheableBitmapDrawable but could not reproduce problem (probably my usage has changed). However my memory told me the problem probably came from nulling. Hence the above change, which I deem healthy.