CurrentIndex does not change when adding items to the beginning of the collection

[dimonovdd]

Platform (please complete the following information):

• OS: [Both]
• Device: [iPhone6/iPhoneSimulator/Pixel/AndroidEmulator and etc]
• Sdk vervion: [any]
• Xamarin.Forms: [any]

Describe the bug
CurrentIndex does not change when adding items to the beginning of the collection

To Reproduce
Steps to reproduce the behavior:

1. Add items to the beginning of the collection
2. Check the value of CurrentIndex