Update BarcodeView for iOS to prevent NullRefrenceException

[EssentialNRG]

BarcodeView.LayoutSubView() still sporadically produces System.NullReferenceException. It looks some kind of race condition. Besides the _previewLayer.Connection I don't see why it throws a null ref exception. I updated the code to create a local copy of the _previewLayer.Connection. Hopefully this is it.

Stacktrace
Unfortunately, the app is build in Release mode, so the line numbers are lost.

int UIApplication.UIApplicationMain(int, string[], IntPtr, IntPtr)
void UIApplication.Main(string[], Type, Type)
void Application.Main(string[] args)

Background
I've got an app that is intensively used by about 55 different users on a daily basis. About one to four times a day the app crashes with this null ref exception. The app already uses the latest 1.5.7 version of the library. It's much better since the release of PR #78, but the issue still remains. It occurs on different devices, ranging from iPhone 8 to 14 with iOS 15.8.2 to 17.6.1.