notify: optimize length check. (#2106)
notify: optimize length check. (#2106)

Signed-off-by: johncming <64aa7c399bffb85fffaccf95be9acb9553c38de5@yahoo.com>
prometheus/alertmanager,GoogleCloudPlatform/alertmanager,GoogleCloudPlatform/alertmanager,GoogleCloudPlatform/alertmanager,GoogleCloudPlatform/alertmanager,prometheus/alertmanager,prometheus/alertmanager,prometheus/alertmanager