Bug 20637: Fix filters content on the holds to pull screen

Bug 20637: Fix filters content on the holds to pull screen

libraries and locations are separated by <br> whereas itypes are using
\n
This patch standardized the separator to generate correctly the filters
pulldown

Test plan:
- Place a hold on a biblio record which has several items
- Define different locations and itypes for these items
- Display the holds on the "Holds to pull" screen and make sure the
filters are working correctly (focus on the dropdown list)

Signed-off-by: Victor Grousset <victor.grousset@biblibre.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>