setting OPENID_PAPE_MAX_AUTH_AGE equal to zero doesn't force reauthentication

[cgreinke]

Taking a look at the code, in OpenIdAuth.setup_request, a max_age of 0 will fail the 'if any(...)' check when preferred_policies and preferred_level_types evaluate to False.

[omab]

@cgreinke, please check the fix. Thanks!

[cgreinke]

Looks good!