title: compass vanishes when MKMap is oriented to north in iOS
body: <p>I am displaying a map on the iPhone using MKMapView. The Map can rotate so that it is oriented with respect to the iPhone orentation using the magnetic heading information. </p>
  
  <p>I like to present the compass but it vanishes each time the map is oriented to north! It reappears when the phone is rotated a little bit further but this is distracting. </p>
  
  <p>The rotation functionality is switched on when some conditions are met like so:</p>
  
  <pre><code>@IBOutlet weak var mapView: MKMapView!
  // here comes some other code
  if settings.useMagneticHeading &amp;&amp; validUserLocation
  {
     mapView.isRotateEnabled = true
     mapView.showsCompass = true
     locationService.startUpdatingHeading()
  }
  </code></pre>
  
  <p>The rotation is performed by a delegate:</p>
  
  <pre><code>func tracingHeading(currentHeading: CLLocationDirection)
  {
      if settings.useMagneticHeading &amp;&amp; validUserLocation
      {
          mapView.camera.heading = currentHeading
          mapView.setCamera(mapView.camera, animated: true)
      }
  }
  </code></pre>
  
  <p>The CoreLocation stuff is encapsulated in the locationService singleton.</p>
  
  <p>How can one force to show the compass also when the map is oriented exactly to north? I guess this behavior is a feature not a bug which seems to be undocumented. (found in iOS 9 and iOS 10)</p>