Bug 36563: Turn into array only if required

Bug 36563: Turn into array only if required

Test plan, apply first patch:
1- Visit item search:
   http://localhost:8081/cgi-bin/koha/catalogue/itemsearch.pl
2- Set "Home library" -> "is not" -> "Centerville". Notice you get items
   from Centerville.
3- Apply second patch, repeat step 2, notice you now don't get items
   from Centervile.
4- Test other use cases, like 'is' and 'is not' for multiple choices

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>