Bug 20838: (bug 16735 follow-up) Fix search by group of libraries

Bug 20838: (bug 16735 follow-up) Fix search by group of libraries

In the last patches of bug 16735, we completely broke the feature!

The limit is using library_groups.id instead of branches.branchcode.

Test plan:
Create a group of library with the search feature
Search (OPAC and staff interfaces) using this limit

=> Without this patch you will see that the generated search query does
not contain branchcodes
=> With this patch applied you will see the branchcodes

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>