Bug 28600: (bug 18989 follow-up) Resolve variable scope issue

Bug 28600: (bug 18989 follow-up) Resolve variable scope issue

This patch fixes a scope issue. Originally, a variable declared as

our $borcat

was replaced by

my $patron

This patch makes the method not rely on global variables, but have a
parameter for the patron, and thus things are clearer.

To test:
1. Open the OPAC detail page for a record
=> FAIL: The logs show some errors about the $patron variable not
available in the scope
2. Apply this patch
3. Repeat 1
=> SUCCESS: No errors
4. Sign off :-D

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>