Bug 14570: (QA follow-up) Call Koha::Patron->find in scalar context

Bug 14570: (QA follow-up) Call Koha::Patron->find in scalar context

This patch prevents opac/opac-memberentry.pl from exploding.

To test:
- Login with a known user in the OPAC
- Open the opac/opac-memberentry.pl page
=> FAIL: It explodes
- Apply this patch
- Restart all the things just in case:
  $ restart_all
- Reload the page
=> SUCCESS: Things work!

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>