WebAccess: fix Access policy page
WebAccess: fix Access policy page

* When CFG_ACCESS_CONTROL_LEVEL_SITE was set to the valid value
  of 3 or CFG_ACCESS_CONTROL_LEVEL_ACCOUNTS was set to the valid
  value of 5, accessing the Access policy page of WebAccess Admin
  interface would have caused an unhandled exception. This is now
  fixed.  Thanks to Alexander Wagner for reporting the problem.
  (closes #656)

tiborsimko/invenio,tiborsimko/invenio,inveniosoftware/invenio,inveniosoftware/invenio