made collections not crash in gallery view

Viewing a collection in gallery view was crashing. This fixes that.

PSU bug: https://scm.dlt.psu.edu/issues/9486
You probably don't want lines 23 & 24 because persisting objects is slow. Just pass a `pid` to the initializer on line 22. You can stub the document list like:

```ruby
assign(:document_list, [SolrDocument.new(@collection.to_solr)])
```