Bug 27849: Koha::Token may access undefined C4::Context->userenv

Bug 27849: Koha::Token may access undefined C4::Context->userenv

The _add_default_csrf_params internal function accesses
C4::Context->userenv without checking that it has been defined. I think
not all of the potential callers of it declare that they require a
defined userenv, so we should test and provide defaults for required
values if it is not defined, to avoid some "Can't use an undefined value
as a HASH reference" HTTP 500 Internal Server Errors.

To test:

Do anything that requires a form with CSRF token, such as editing your
details. Behaviour should be unchanged. To test the failure case, you
would need some customised code that indirectly generates a CSRF token
before setting the userenv up and I am not sure there is any in released
Koha yet.

Signed-off-by: Paul Derscheid <paul.derscheid@lmscloud.de>
Looks good to me. Working as expected.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>