Checking for errors in mailman-api before using results

Signed-off-by: Alexandre Barbosa <alexandreab@live.com>
Signed-off-by: Macartur Sousa <macartur.sc@gmail.com>
Signed-off-by: Sergio Oliveira <sergio@tracy.com.br>

colab/accounts/utils/mailman.py

@@ -139,7 +139,12 @@ def list_users(listname):
     except requests.exceptions.RequestException:
         return []
 
-    return users.json()
+    result = users.json()
+    if isinstance(result, int):
+        LOGGER.error('Error number %s', result)
+        return []
+
+    return result
 
 
 def get_user_mailinglists(user):