BUG/MEDIUM: mailers: make sure to always apply offsets to now_ms in expiration

Now_ms can be zero nowadays, so it's not suitable for direct assignment to
t->expire, as there's a risk that the timer never wakes up once assigned
(TICK_ETERNITY). Let's use tick_add(now_ms, 0) for an immediate wakeup
instead. The impact here might be mailers suddenly stopping.

This should be backported where it applies.

Author: wtarreau

src/mailers.c

@@ -80,7 +80,7 @@ static struct task *process_email_alert(struct task *t, void *context, unsigned
 
 			alert = LIST_NEXT(&q->email_alerts, typeof(alert), list);
 			LIST_DELETE(&alert->list);
-			t->expire             = now_ms;
+			t->expire             = tick_add(now_ms, 0);
 			check->tcpcheck_rules = &alert->rules;
 			check->status         = HCHK_STATUS_INI;
 			check->state         |= CHK_ST_ENABLED;