Bug 17743: Item search - Fix indexes build on MARC

Bug 17743: Item search - Fix indexes build on MARC

Searching items by custom search fields does not work because these
fields are not correctly processed in JS.

In case of custom search field, the parent of the option is not the
select but the optgroup element.

Test plan:
Create a custom search field on 245$c for instance
On the items search form, select this field and launch a search
=> Without this patch, the results will not be filtered and you will get
all your items
=> With this patch applied, the results should be correctly filtered

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Mason James <mtj@kohaaloha.com>