Bug 9341: Problem with UNIMARC authors facets

Bug 9341: Problem with UNIMARC authors facets

In UNIMARC installations the authors have a double comma separating the subfield a and the subfield b.

Test plan:

- After applying the patch do a search and check the double comma in authors facets.
- Apply the patch
- Do a new search
- Check if authors facets as a double comma

Sponsored-by: KEEP SOLUTIONS
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>
Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>