Bug 11208: regression test for failing SMS messages

Bug 11208: regression test for failing SMS messages

This patch adds a regression test for verifying that queued
SMS messages meant for patrons who have no SMS alert number
set are marked as failed after the first attempt to send them.

To test:

[1] Run prove -v t/db_dependent/Letters.t.  The fourth
    test should.
[2] Apply the main patch and run t/db_dependent/Letters.t
    again.  This time, all tests should pass.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
(cherry picked from commit b753678c3dff4e0fd2fde008b3c43f0796fcfb05)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>