Bug 26114: ILL should mark status=RET only if a return happened

Bug 26114: ILL should mark status=RET only if a return happened

The original code assumed every codepath should be trated as a
successful check-in. Such is not the case and the regression tests
verify that the code acknowledges this.

To test:
1. Apply the regression tests patch
2. Run:
   $ kshell
  k$ prove t/db_dependent/Illrequests.t
=> FAIL: Tests fail
3. Apply this patch
4. Repeat 2
=> SUCCESS: Tests pass!
5. Sign off :-D

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>