The API for this is a bit strange due to the caching that we're doing.  When we call `document.collection_members.present?` here we actually cache the solr query (even through we're not touching the docs yet). Since this solr query is cached w/ the default rows (if none given) this will return 20 (or all the files if less than 20).  I was a bit worried this would happen, but figured we would deal w/ it when it came up.

I believe that the desire is to only show 3 for file collections (at least that's what I gathered from the mockups).

Given that, we'll need to pass a rows parameter to make sure that if our `#present?` call is the first one to cache the query that it returns the rows we expect when dealing w/ file collections. (e.g. https://github.com/sul-dlss/SearchWorks/blob/master/app/views/catalog/_file_collection_members.html.erb#L2 ).

We can look at other alternatives for dealing w/ this (one idea is a `no_cache: true` option, but that would be less performant) but since we know that we want 3 files for file documents, and we have object specific partials, maybe this will just work.