fix(dynamic_component_loader): leave the view tree in a consistent state when hydration fails

Closes #5718

modules/angular2/src/core/change_detection/abstract_change_detector.ts

@@ -169,7 +169,7 @@ export class AbstractChangeDetector<T> implements ChangeDetector {
   // any work done in `hydrateDirectives`.
   dehydrateDirectives(destroyPipes: boolean): void {}
 
-  hydrated(): boolean { return this.context !== null; }
+  hydrated(): boolean { return isPresent(this.context); }
 
   afterContentLifecycleCallbacks(): void {
     this.dispatcher.notifyAfterContentChecked();