Make sure only subscribed users recieve welcome emails

[MAILPOET-2331]

lib/Cron/Workers/SendingQueue/SendingQueue.php

@@ -88,6 +88,7 @@ class SendingQueue {
         } else {
           // No segments = Welcome emails
           $found_subscribers = SubscriberModel::whereIn('id', $subscribers_to_process_ids)
+            ->where('status', SubscriberModel::STATUS_SUBSCRIBED)
             ->whereNull('deleted_at')
             ->findMany();
           $found_subscribers_ids = SubscriberModel::extractSubscribersIds($found_subscribers);