title: UNUserNotificationCenter.current().getDeliveredNotifications only ever returns an empty array
body: <p>Basically, I'm simply trying to print the notifications that my app has delivered, but doing something like:</p>
  
  <pre><code>UNUserNotificationCenter.current().getDeliveredNotifications { (notifications) in
      print(notifications)
  }
  </code></pre>
  
  <p>just displays an empty array in the Xcode console, even when the notification center contains several delivered notifications. (<code>print(notifications.count)</code> returns 0)</p>
  
  <p>I can use <code>getPendingNotificationRequests</code> to successfully grab the notifications that are scheduled yet undelivered, update them, and even remove them with <code>removePendingNotificationRequests(withIdentifiers:)</code>. But any attempt to access/modify/remove anything that's been delivered does not work. </p>
  
  <p>Am I missing something simple here? Did something change recently with the way iOS 10+ accesses the delivered notifications?</p>