Bug 22016: Always send CT field for SIP checkin, even if empty

Bug 22016: Always send CT field for SIP checkin, even if empty

Some SIP devices ( in this particular case, bin sorting machines from RFID Library Solutions ) require a CT field to be sent, even if that field is empty. Koha should be able to support this behavior.

Test Plan:
1) Apply this patch
2) Enable the new option ct_always_send for a SIP2 account
3) Restart SIP
4) Check in an item successfully via SIP, which will not be transferred
5) Note the response contains a CT field with no value

Sponsored-by: Pueblo City-County Library District
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jill Kleven <jill.kleven@pueblolibrary.org>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>