Bug 21535: Anonymize function in Patron should not scramble email addresses

Bug 21535: Anonymize function in Patron should not scramble email addresses

Scrambled email addresses will only generate warnings etc.
Clear them although they might be in BorrowerMandatoryField.

Test plan:
Run t/db_dependent/Koha/Patrons.t

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Owen Leonard <oleonard@myacpl.org>
t/db_depepended/Koha/Patrons.t runs with no warnings.

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>