Bug 31535: Fix warning - uninitialized value for location

Bug 31535: Fix warning - uninitialized value for location

In Koha/Item.pm line 169 (line number has been changed)

Test plan:
You need location to be NULL when storing.
Otherwise follow this reasoning:
  What happens when location is undefined? It is autovivified to
  empty string in the string compare (ne), so not equal to CART
  and PROC. The subcondition is true before and after this patch.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Joonas Kylmälä <joonas.kylmala@iki.fi>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>