MAE-318: Handle edge case when the job executed twice

If the job executed during the execution of the queue, there will be
repeated tasks in the queue and this commit fix it and only adds tasks
when the queue is empty.

CRM/MembershipExtras/Job/OfflineAutoRenewal.php

@@ -8,8 +8,14 @@ class CRM_MembershipExtras_Job_OfflineAutoRenewal {
 
   private $queue;
 
+  /**
+   * @var int
+   */
+  private $numberOfQueueItems;
+
   public function __construct() {
     $this->queue = OfflineAutoRenewalQueue::getQueue();
+    $this->numberOfQueueItems = (int) $this->queue->numberOfItems();
   }
 
   /**
@@ -19,7 +25,9 @@ public function __construct() {
    * @return True
    */
   public function run() {
-    $this->addTasksToQueue();
+    if ($this->numberOfQueueItems === 0) {
+      $this->addTasksToQueue();
+    }
     $this->runQueue();
 
     return TRUE;