make sure ABSPATH is defined before using it - fixes issue #648

lib/Cron/Daemon.php

@@ -1,4 +1,6 @@
 <?php
+if(!defined('ABSPATH')) exit;
+
 namespace MailPoet\Cron;
 
 use MailPoet\Cron\Workers\Scheduler as SchedulerWorker;
@@ -6,8 +8,6 @@ use MailPoet\Cron\Workers\SendingQueue\SendingQueue as SendingQueueWorker;
 
 require_once(ABSPATH . 'wp-includes/pluggable.php');
 
-if(!defined('ABSPATH')) exit;
-
 class Daemon {
   public $daemon;
   public $request_data;