Open Radar

 
Summary:
When accessing the `connection` instance property on an `AVCaptureVideoPreviewLayer` instance, the app will always crash. Accessing other instance properties succeeds.

Steps to Reproduce:
1. Create an instance of AVCaptureVideoPreviewLayer
2. Attempt to access the connection property on the new instance (by any method to unwrap the optional)
3. Attempt to load onto your iOS 10 beta device
4. Notice how it throws a fatal error and aborts the app while trying to access that property:

```
fatal error: unexpectedly found nil while unwrapping an Optional value
```

Expected Results:
I expect to either access the property or to skip it via unwrapping.

Actual Results:
Regardless of unwrapping or not, the app aborts and throws a fatal error.

Version:
10.0 (14A5322e)

Notes:
Example code:

```
previewLayer = AVCaptureVideoPreviewLayer(session: CameraManager.captureSession) as AVCaptureVideoPreviewLayer

previewLayer?.connection.videoOrientation = AVCaptureVideoOrientation.LandscapeRight
previewLayer?.frame = imageView.bounds
previewLayer?.videoGravity = AVLayerVideoGravityResizeAspectFill
previewLayer?.mask = maskLayer

imageView.layer.addSublayer(previewLayer!)

dispatch_async(CameraManager.sessionQueue) { () -> Void in
  CameraManager.captureSession.startRunning()
}
```

Configuration:
iPhone 6 128gb