fix(windowWhen): fix windowWhen with regard to unsubscriptions

Fix windowWhen operator to unsubscribe the closingNotification observable when the source has raised
an error or has completed, or received an explicit unsubscribe() call. Also change windowWhen to
close a window whenever the closingNotification completes, this is aligned with how windowToggle
behaves as well.

src/operators/windowWhen.ts

@@ -37,11 +37,25 @@ class WindowSubscriber<T> extends Subscriber<T> {
   _error(err: any) {
     this.window.error(err);
     this.destination.error(err);
+    this._unsubscribeClosingNotification();
   }
 
   _complete() {
     this.window.complete();
     this.destination.complete();
+    this._unsubscribeClosingNotification();
+  }
+
+  unsubscribe() {
+    super.unsubscribe();
+    this._unsubscribeClosingNotification();
+  }
+
+  _unsubscribeClosingNotification() {
+    let closingNotification = this.closingNotification;
+    if (closingNotification) {
+      closingNotification.unsubscribe();
+    }
   }
 
   openWindow() {
@@ -84,6 +98,6 @@ class WindowClosingNotifierSubscriber<T> extends Subscriber<T> {
   }
 
   _complete() {
-    // noop
+    this.parent.openWindow();
   }
 }