Protect access to mWebView by checking mRunnable.

If the user cancels the login event, mRunnable will be reset and the WebView
destroyed.  Check for a null mRunnable before accessing mWebView.

Bug: 3361009
Bug: 3349815
Change-Id: Idd9a2b788673d9ec95bfa083a4af7df705c22fcd
1 file changed