Bug 29914: (QA follow-up) Add comment to explain last case

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>

JD amended patch: remove ref to line number

(cherry picked from commit a866722ae6)
Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>

C4/Auth.pm

@@ -1842,6 +1842,8 @@ sub check_cookie_auth {
         } else {
             return ( "anon", $session );
         }
+        # If here user was logged in, but doesn't have correct permissions
+        # could be an 'else' at `if($flags) return "ok"` , but left here to catch any errors
         $session->delete();
         $session->flush;
         C4::Context->_unset_userenv($sessionID);