fix(groupBy): durationSelector cannot keep source alive

Fix test case "Observable.prototype.groupBy() should return inner that does not throw when faulty outer is
unsubscribed early". The Observable given as argument to the
durationSelector of groupBy should not participate in the refCounting of
the outer Observable.

src/operators/groupBy-support.ts

@@ -30,13 +30,13 @@ export class RefCountSubscription<T> extends Subscription<T> {
 export class GroupedObservable<T> extends Observable<T> {
   constructor(public key: string,
               private groupSubject: Subject<T>,
-              private refCountSubscription: RefCountSubscription<T>) {
+              private refCountSubscription?: RefCountSubscription<T>) {
     super();
   }
 
   _subscribe(subscriber: Subscriber<T>) {
     const subscription = new Subscription();
-    if (!this.refCountSubscription.isUnsubscribed) {
+    if (this.refCountSubscription && !this.refCountSubscription.isUnsubscribed) {
       subscription.add(new InnerRefCountSubscription(this.refCountSubscription));
     }
     subscription.add(this.groupSubject.subscribe(subscriber));

src/operators/groupBy.ts

@@ -69,7 +69,7 @@ class GroupBySubscriber<T, R> extends Subscriber<T> {
         let groupedObservable = new GroupedObservable<R>(key, group, this.refCountSubscription);
 
         if (durationSelector) {
-          let duration = tryCatch(durationSelector)(groupedObservable);
+          let duration = tryCatch(durationSelector)(new GroupedObservable<R>(key, group));
           if (duration === errorObject) {
             this.error(duration.e);
           } else {