Bug 19214: Prevent crash if ->club or ->patron is called in list context

Bug 19214: Prevent crash if ->club or ->patron is called in list context

To test:
1) Create a club template and a club.
2) Add a user to the club
3) Log in to the OPAC as that user
4) Go to 'your summary' and click the Clubs tab
5) Notice clubs do not load and a warn shows:
Template process failed: undef error - Cannot use "->find" in list
context at /home/vagrant/kohaclone/Koha/Club/Enrollment.pm line 62.
6) Go to the staff side and go to the member page of that user
7) Go to 'details' and click the Clubs tab
8) Notice clubs do not load and a warn shows:
Template process failed: undef error - Cannot use "->find" in list
context at /home/vagrant/kohaclone/Koha/Club/Enrollment.pm line 71.
9) Apply patch
1) Repeat steps 4-7, confirming the errors do not show and clubs info
loads correctly

Sponsored-by: Catalyst IT
Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>