Fix search results below fold not being rendered on scroll since v0.149.0

In Atom `v0.153.0` search results are not being appended when you try to scroll below the fold. #272 looks like exactly this problem so I didn't create a separate issue.

Looking in the spec it looks like [this test](https://github.com/atom/find-and-replace/blob/9a1a5ec9cc3964f8987b89a4eff890abea7a2922/spec/results-view-spec.coffee#L102-L124) should be catching it, but it didn't. So... cc @benogle :grimacing: