fix($ionNavView): prevent read property 'name' of null

Sometimes, absolutely spontaneously, I have the error:
```
TypeError: Cannot read property 'name' of null
    at IonicModule.directive.directive.compile (http://localhost:8000/ios/www/bower_components/ionic/release/js/ionic.bundle.js:40819:79)
    at nodeLinkFn (http://localhost:8000/ios/www/bower_components/ionic/release/js/ionic.bundle.js:15111:13)
    at compositeLinkFn (http://localhost:8000/ios/www/bower_components/ionic/release/js/ionic.bundle.js:14517:15)
    at publicLinkFn (http://localhost:8000/ios/www/bower_components/ionic/release/js/ionic.bundle.js:14426:30)
    at updateView (http://localhost:8000/ios/www/bower_components/ionic/release/js/ionic.bundle.js:40883:11)
    at IonicModule.directive.directive.compile.eventHook (http://localhost:8000/ios/www/bower_components/ionic/release/js/ionic.bundle.js:40827:17)
    at Scope.$get.Scope.$broadcast (http://localhost:8000/ios/www/bower_components/ionic/release/js/ionic.bundle.js:21142:28)
    at $state.transitionTo.$state.transition.resolved.then.$state.transition (http://localhost:8000/ios/www/bower_components/ionic/release/js/ionic.bundle.js:33927:22)
    at deferred.promise.then.wrappedCallback (http://localhost:8000/ios/www/bower_components/ionic/release/js/ionic.bundle.js:19846:81)
    at http://localhost:8000/ios/www/bower_components/ionic/release/js/ionic.bundle.js:19932:26 <ion-nav-view> 
```
This happens because of attempt to read 'name' property of parent.state where state=null. Looks like not only me have this error (http://forum.ionicframework.com/t/how-do-i-get-rid-of-this/3674). So it will be good to rid of it.