Bug 25769: Patron self modification triggers change request for date of birth to...

Bug 25769: Patron self modification triggers change request for date of birth to null

If PatronSelfModificationBorrowerUnwantedField contains dateofbirth, all
patron self modification requests will attempt to set dateofbirth to
null instead of ignoring the field.

Test Plan:
1) Add dateofbirth to PatronSelfModificationBorrowerUnwantedField
2) Run a patron self modification
3) Note the request sets dateofbirth to null on the staff side
4) Apply this patch
5) Restart all the things!
6) Run another self-modification
7) Note of the staff side that dateofbirth is unaffected

Signed-off-by: Emmi Takkinen <emmi.takkinen@outlook.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>