bug 614150: bail out on ACTOR_USER_NOT_FOUND

bug 614150: bail out on ACTOR_USER_NOT_FOUND

This fixes a bug where uploading an offline checkout
that refers to a missing patron returns an INTERNAL_SERVER_ERROR
instead of ACTOR_USER_NOT_FOUND.  More generally, this avoids
an exception in case case where a circ operation is made
without checking the existence of the patron record beforehand.

mk_env could use a better name, too.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
git-svn-id: svn://svn.open-ils.org/ILS/branches/rel_1_6_1@17115 dcc99617-32d9-48b4-a31d-7c20da2025e4