[PR3] Navigationview : incorrect behavior of back button

[freelance]

When using a navigation view and useTitleForBackButtonText: true, the back button fails to disappear in the first (topmost) view.
Steps to reproduce :

• Open the navigationview example
• Push button on toolbar (rightbottom)
• Select "Toggle back button text"
• Select "Push another view!"
• Select "Back"

Result : Back button stays on screen.

[Jamie Avins]

Thank you for the report.