Bug 18461: Make tests break on wrong UTF8 data handilng

Bug 18461: Make tests break on wrong UTF8 data handilng

This patch makes the tests fail if extended attributes handling fails due to
wrong UTF-8 data handling.

To test:
- Run:
  $ sudo koha-shell kohadev
 k$ cd kohaclone
 k$ prove t/db_dependent/Koha/Patron/Modifications.t
=> FAIL: Tests explode

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>