title: PendingIntent.FLAG_UPDATE_CURRENT recreates Activity
body: <p>I have a notification and when I tap it I want to launch application if it is still not running, but if application already running, I do not want to relaunch it.
  So, I am using <code>PendingIntent.FLAG_UPDATE_CURRENT</code> flag when creating <code>PendingIntent</code>. </p>
  
  <p>My code:</p>
  
  <pre><code>private val notificationManager by lazy { NotificationManagerCompat.from(this) }
  
  fun testPush() {
          val notificationBuilder = NotificationCompat.Builder(this, BuildConfig.APPLICATION_ID)
                  .setSmallIcon(R.drawable.ill_launcher)
  
          notificationBuilder
                  .setContentTitle("Title")
                  .setContentText("Test text")
                  .setContentIntent(buildPendingIntent())
  
          notificationBuilder
                  .setAutoCancel(true)
                  .priority = NotificationCompat.PRIORITY_DEFAULT
  
          notificationManager.notify(1, notificationBuilder.build())
  }
  
   private fun buildPendingIntent(): PendingIntent {
  
          val intent = Intent(this, RootActivity::class.java)
          intent.flags = Intent.FLAG_ACTIVITY_SINGLE_TOP
          intent.putExtra("action", RootActivity.DEFAULT_INTENT)
  
          return PendingIntent.getActivity(this, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT)
  }
  </code></pre>
  
  <p>But when I launch the application and click on the notification, the activity is recreates.</p>