title: ReactNative WebView onNavigationStateChange is NOT triggered when going back
body: <p>I have a react native app with a WebView. I have implemented navigation in the webview such as going back to previous screen using goBack() function of the webview. But the problem is I want the back icon disabled when the user reaches the home page in the webview. </p>
  
  <p>Initially canGoBack prop is false on webview home page but after few navigations and coming back to home page doesn't set canGoBack to false.Hence back button is still enabled but othing happens when clicked.</p>
  
  <p>Interestingly onNavigationStateChange also doesn't get triggered when going back. It only fires when clicking on links or navigating to other pages in the webview. Anyone has any solution as to how to disable custom back button on home page?</p>