Bug 33578: Fix patron restriction types edition

Bug 33578: Fix patron restriction types edition

When editing an existing patron restriction type you'll always get an error on saving:

Label is already in use

To test:
* Activate use of patron restriction types
* Edit any of the system types
* Create new ones

Signed-off-by: Michaela Sieber <michaela.sieber@kit.edu>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
(cherry picked from commit 9e32945f208fa16c773dfc0867754649fcf820ca)
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>