Bug 14760: Disabled courses display in the course reserves list for items

Bug 14760: Disabled courses display in the course reserves list for items

If an item is on reserve for two courses but one of those courses is
disabled, both courses are still listed on opac-detail.pl!

Test Plan:
1) Enable course reserves
2) Create two courses
3) Place one item on reserve for both courses
4) Disable one of the two courses
5) View the record details for that record/item
6) You should see both courses listed in the course reserves column
7) Apply this patch
8) Reload the page
9) You should now only see the active course in the course reseves column

Followed test plan. Works as expected.
Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>