Avoid infinite recursion, but allow the app to handle the error somewhat

Signed-off-by: Joshua Peek <josh@joshpeek.com>

lib/rack/openid.rb

@@ -91,7 +91,7 @@ def begin_authentication(env, qs)
           return redirect_to(url)
         rescue ::OpenID::OpenIDError, Timeout::Error => e
           env[RESPONSE] = MissingResponse.new
-          return self.call(env)
+          return @app.call(env)
         end
       end