Initial resourceVersion if initialState is used

[shawkins]

The change to allow an initial cached listing for informers does not take into account the possibility of using initialState - since initialState is being specified without the last known resource version there's a chance that we're listing from before the initial state. This can lead to some undesirable events until things are caught up. Rather than trying to make the user track the last resource version, which may also require some additional locking to be done in a foolproof way, we should just use the latest listing instead.