Make app always call applicationWillTerminate

AppDelegate.swift

  func applicationDidEnterBackground(application: UIApplication) {
    // Create a pseudo background task to system call applicationWillTerminate when app enter background
    // Default system will not call applicationWillTerminate when app enter background
    // applicationWillTerminate only called when user close app in app switcher or some special cases of system
    bgTask = application.beginBackgroundTaskWithExpirationHandler({ () -> Void in
      application.endBackgroundTask(self.bgTask)
      self.bgTask = UIBackgroundTaskInvalid
    })

    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)) { () -> Void in
      self.bgTask = UIBackgroundTaskInvalid
      application.endBackgroundTask(self.bgTask)
    }
  }

@quangtqag @Hazoomo @killann why do you "override" bgTask and use application.endBackgroundTask(UIBackgroundTaskInvalid)?