Use more generic False-y check

This will prevent redirect loops with the strict validation disabled

Co-authored-by: Giuseppe De Marco <[email protected]>

Author: tymees

djangosaml2/views.py

@@ -575,7 +575,7 @@ def post(self, request, attribute_mapping=None, create_unknown_user=None):
             return HttpResponseRedirect(custom_redirect_url)
 
         relay_state = validate_referral_url(request, relay_state)
-        if relay_state is None:
+        if not relay_state:
             logger.debug(
                 "RelayState is not a valid URL, redirecting to fallback: %s",
                 relay_state