Bug 6694: Problem with casAuthentication syspref

Bug 6694: Problem with casAuthentication syspref

A missing test in checkauth caused anonymous session to be destroyed and
re-created at every call when this syspref was set.
Almost the same issue is also fixed in check_api_auth, which caused
C4::Service->init to fail.

Signed-off-by: Alex Arnaud <alex.arnaud@biblibre.com>
Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>
(cherry picked from commit 8ffbf4e88c6ed98ad697bb4a2b4d9d1456d2c84c)

Signed-off-by: Chris Nighswonger <chris.nighswonger@gmail.com>