Bug 31186: Fix the hidingrules test for result numbering

Bug 31186: Fix the hidingrules test for result numbering

We should not test the $hidingrules variable but the number
of keys it contains.

Test plan:
Clear OpacHiddenItems.
Check with and without this patch search result numbering on
the OPAC.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
(cherry picked from commit d7647052f20104b70ba6b02d1535874fb9ab3b61)

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>