Bug 26506: Fix Koha::Account::pay if called when no user is logged-in

Bug 26506: Fix Koha::Account::pay if called when no user is logged-in

Currently, Koha::Account::pay will fail if no user is logged-in when it is
called.

In this case, this patch will use undef instead of 0 for $manager_id in order
to comply with the foreign key constraint on manager_id.

Signed-off-by: Magnus Enger <magnus@libriotech.no>
Biblibre and Libriotech have created a OPAC payment plugin that was
having problems because of this bug. Applying the fix in this patch
to a live server solved the problem.
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>