Bug 33620: Don't show guarantor info on details page if borrowerRelationship is empty

Bug 33620: Don't show guarantor info on details page if borrowerRelationship is empty

To test:
1. Apply patch
2. Have some values in borrowerRelationship.
3. Go to a patron details page and see both 'Show checkouts to guarantor:' and 'Show charges to guarantor:'
4. Now empty borrowerRelationship.
5. Visit the patron detail page again and you should no longer see either of those fields.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>