Bug 13779: (QA follow-up) Correct checkauth call in offline_circ/download.pl

Bug 13779: (QA follow-up) Correct checkauth call in offline_circ/download.pl

Script offline_circ/download.pl does not use the return values of
checkauth. So should not assign them to bad chosen variables that do
not correspond with checkauth but with get_template_and_user.

Test plan:
Look for $template, $loggedinuser, $cookie, $flags in the code.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>