title: num_cart_items returns empty
body: <p>I'm using the IPN simulator to post the data to my IPN handler. Everything else comes out fine, except for this.</p>
  
  <pre><code>$num_cart_items = $_POST['num_cart_items'];
  
  $tuotteet = array();
  for($i = 1; $i &lt;= $num_cart_items; $i++) {
      $tuotteet[] = array('nimi'=&gt;$_POST['item_name' . $i], 'maara'=&gt;$_POST['quantity' . $i]);
  }
  $products = implode(" ", array_map(function ($entry) { return $entry['maara'].'x '.$entry['nimi'].'&lt;br /&gt;'; }, $tuotteet));
  </code></pre>
  
  <p>When I try to save $products to a database, I get empty value. I also tried saving the $num_cart_items and that shows up as empty too.</p>