Non-primary authors cannot be filtered with biblio search when sorted by Author

Problem/Motivation

When multiple authors exist on a biblio citation, all secondary authors will not be able to be found as part of a "filter" from the biblio search if the search is sorted by Author name.

Steps to reproduce

1. setup a site with biblio installed
2. Turn on biblio search
3. create an entry with more than one "contributor" or author (the category and role selected are unimportant, for the sake of this situation, feel free to just leave them as "Primary" and "Author") (or import the xml file I link to below after turning on the Biblio Endnote XML Import/Export submodule)
4. go to the "biblio" page to see "all" of the entries
5. sort the results by author name
6. either click on a secondary author/contributor or select a secondary author/contributor from the filter box in the search tools

You should see that any citation where the author is the secondary author/contributor will not show up in the citation search result listing when the sort is by Author.

Proposed resolution

Include secondary authors/contributors in the results even when sorting by author name (which would sort only by the primary author's name).