Bug 19315: Use bibnum instead of biblionumber in routing-preview.pl and add item...

Bug 19315: Use bibnum instead of biblionumber in routing-preview.pl and add item check

To test:
 1 - Create a serial subscription attached to a record
 2 - Receive some issues
 3 - Edit the subscription
 4 - Go to serails collection
 5 - Try to print a routing list
 6 - You may or may not get the right serial
 7 - Additionally create a subscription attached to a bib with no items
 8 - Try to print a routing list for this serial
 9 - You will get 'Internal server error'
10 - Apply patch
11 - Print routing list for first serial
12 - You will always get the correct bib
13 - Print routing list for second serial
14 - You should no longer get an error

Signed-off-by: Caroline Cyr La Rose <caroline.cyr-la-rose@inlibro.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>