Bug 18422: (QA follow-up) Check if select2 is available before using it

Bug 18422: (QA follow-up) Check if select2 is available before using it

cataloging.js might not always be loaded with select2.js, so we should
check its availability to prevent JS errors

Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
(cherry picked from commit 56a0aabc58a3475912894523cc92757153b967bd)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>
(cherry picked from commit 1d450ad13a6bcd8f4f826bae7290a3184564badb)
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>