Bug 13976: Sort popularity numerically in Zebra

Bug 13976: Sort popularity numerically in Zebra

To test:
1 - Create a new template at Tools->Marc modification template
2 - Add action: Copy 999$c to 942$0
3 - Create a report:
    SELECT biblionuber FROM biblios
4 - Run report, show all, do a batch modification to all records using template above
5 - Search for 'a' (make sure you are using Zebra)
6 - Sort by popularity
7 - Note records are sorted wrong
8 - Apply patch
9 - Restart all
10 - Reload search results
11 - Success! Sorted correctly

Signed-off-by: Anke <anke.bruns@gwdg.de>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>