Bug 34857: Do not enable hidden select element (regression from bug 33233).

Bug 34857: Do not enable hidden select element (regression from bug 33233).

Test plan:

Using Chrome as web browser:

* Go to opac advanced search
* Press "more options"
* Search for two keywords using "and" operator (on ktd search for idea AND behind, which matches 1 result)
* Search for two keywords using "or" operator (on ktd search for idea OR behind, which matches 4 results)
* Search for two keywords using "not" operator (on ktd search for idea NOT behind, which matches 2 results)

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>