Fix post notifications to work with dynamic segments

[PREMIUM-38]

lib/Cron/Workers/Scheduler.php

@@ -7,6 +7,7 @@ use MailPoet\Models\Newsletter;
 use MailPoet\Models\SendingQueue;
 use MailPoet\Models\Subscriber;
 use MailPoet\Models\SubscriberSegment;
+use MailPoet\Segments\SubscribersFinder;
 use MailPoet\Util\Helpers;
 use MailPoet\Newsletter\Scheduler\Scheduler as NewsletterScheduler;
 
@@ -73,12 +74,11 @@ class Scheduler {
     if(empty($segments)) {
       return $this->deleteQueueOrUpdateNextRunDate($queue, $newsletter);
     }
-    $segment_ids = array_map(function($segment) {
-      return (int)$segment['id'];
-    }, $segments);
 
     // ensure that subscribers are in segments
-    $subscribers = Subscriber::getSubscribedInSegments($segment_ids)->findArray();
+
+    $finder = new SubscribersFinder();
+    $subscribers = $finder->getSubscribersByList($segments);
     $subscribers = Helpers::flattenArray($subscribers);
 
     if(empty($subscribers)) {

lib/Segments/SubscribersFinder.php

@@ -29,6 +29,7 @@ class SubscribersFinder {
         return $subscribers;
       }
     }
+    return array();
   }
 
   function getSubscribersByList($segments) {
@@ -50,6 +51,7 @@ class SubscribersFinder {
         return $subscribers;
       }
     }
+    return array();
   }
 
   private function unique($subscribers) {