Steps to reproduce:

1. Enable LDAP authentication and create an LDAP server.
2. Disable LDAP authentication.
3. Using API send authentication.update request:

   {
     "jsonrpc": "2.0",
     "method": "authentication.update",
     "params": {
       "ldap_userdirectoryid": 0,
       "ldap_auth_enabled": 1
     },
     "id": 1
   }

Result:
config table is successfully updated, no error message.
Expected:
Error should be thrown, stating either default LDAP server should be set, or that provided user directory does not exist.