Fix "page goes blank after saving" bug

This was breaking if your internet was fast. ;)
Fade-out of the web view to the progress indicator was getting
canceled by the subsequent fade-in, but the listener's onAnimationEnd
handler was still being called and hiding the webView completely.

Added a check for cancelation, which seems to resolve it.

Bug: 60696
Change-Id: I226568aa43fd5720af34ce285d6136b702b881c5