If .cache() is called after fully rendered we may have to update the height

[wilsonpage]

If the user is using appending chunks pattern and calls .cache() after the finally chunk has fully rendered the height of the list may be incorrect.

This is because we instantly set the fullHeight from the last cache. When we cache next, it an indication that the model is now complete. If this happens before the fastlist.render() it's OK as the cached height will be cleared before the render takes place.

If it's called after the final fastlist.render() then we risk not updating the list height and it could remain locked at the old height.

When the user calls .cache() we should check the calculated height against the list's current actual height and update if they don't match.