emptyView not visible when using two section controllers

I'm using `IGListKit` in a way similar to the [Load More example](https://github.com/Instagram/IGListKit/blob/6c64c54a32a4d81063caa9dad14e7149d0a527ad/Examples/Examples-iOS/IGListKitExamples/ViewControllers/LoadMoreViewController.swift). I have a separate section controller for a separate view on top and a section controller for the data below. When there is no data, I have confirmed the `emptyView(for listAdapter: ListAdapter)` callback is hit but when I return a view such as a `UILabel`, it is not visible. However if I remove the top section, it is visible. So issue is narrowed down. Is there anything else I need to do to get this view to show?

## New issue checklist

- [x] I have reviewed the [`README`](https://github.com/Instagram/IGListKit/blob/master/README.md) and [documentation](http://instagram.github.io/IGListKit)
- [x] I have searched [existing issues](https://github.com/Instagram/IGListKit/issues) and this is not a duplicate

### General information

- `IGListKit` version: 3.4.0
- Related issues: #1114