Bug 18620 - t/db_dependent/Letters.t failing on master

Bug 18620 - t/db_dependent/Letters.t failing on master

To test:
1 - Set SMSSenDriver to 'Email'
2 - prove t/db_dependent/Letters.t
3 - Tests fail
4 - Apply patch
5 - prove t/db_dependent/Letters.t
6 - Less tests fail (should be 2 sms test failures)
7 - Set SMSSendDriver to another value or blank
8 - prove t/db_dependent/Letters.t
9 - Tests pass

Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>