Bug 26271: Add failing test to reveal issue with patrons API endpoint

Bug 26271: Add failing test to reveal issue with patrons API endpoint

When manager_id is null/undef the API returns error code 500.

To test:
 1) Notice failure when running
    prove t/db_dependent/api/v1/patrons_accounts.t

Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
(cherry picked from commit 898cd3b82ee84682bdfad1c177e2eb6ae0881428)

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>