Bug 18025 - Expired password recovery links cause sql crash

Bug 18025 - Expired password recovery links cause sql crash

When a user gets an email, but doesn't act or visit it within two days,
     attempting to create a new one causes a collision. We should just
     delete the old one, assuming they still want to reset their
     password.

To test:
create yourself a borrower with a userid and password.
Attempt a password recovery on the OPAC
update the entry in the database for that user to have an expired token
e.g. update borrower_password_recovery set valid_until = '2017-01-25
03:25:26' where borrowernumber = 12;
Attempt another password recovery operation - should error
apply the patch
Try it again - no error, new token is generated and additional email
with new link is sent.

Issue reproduced - is resolved by patch
Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Mason James <mtj@kohaaloha.com>