Invert Not Enforced does not work if Not Enforced URLs list is empy

Steps to reproduce:

1. Configure Agent with `Invert Not Enforced URLs` enabled.
2. Confirm `Not Enforced URLs` contains no entries (the default).
3. Access a URL such as 'http://agent.exampe.com/unprotected'

Expected result:
'http://agent.exampe.com/unprotected' is not protected.

Actual result:
Redirected for authentication.

Workaround:
Add an entry to the 'Not Enforced URLs' list, such as 'http://agent.exampe.com/dummy'.