LP#1241644: Remove xact_finish IS NULL checks from CLAIMSRETURNED and LONGOVERDUE

Makes open-ils.actor.user.checked_out(.count) results agree with
open-ils.storage.actor.user.checked_out(.count) results.

Signed-off-by: Jason Boyer <jboyer1@library.in.gov>
Signed-off-by: Michele Morgan <mmorgan@noblenet.org>
Signed-off-by: Ben Shum <bshum@biblio.org>