fix(race): handle observables completes immediately

closes ReactiveX#1615

spec/operators/race-spec.ts

@@ -1,3 +1,4 @@
+import {expect} from 'chai';
 import * as Rx from '../../dist/cjs/Rx';
 declare const {hot, cold, expectObservable, expectSubscriptions};
 
@@ -147,4 +148,13 @@ describe('Observable.prototype.race', () => {
     expectSubscriptions(e1.subscriptions).toBe(e1subs);
     expectSubscriptions(e2.subscriptions).toBe(e2subs);
   });
+
+  it('should allow observable emits immediately', (done: MochaDone) => {
+    const e1 = Observable.of(true);
+    const e2 = Observable.timer(200).map(_ => false);
+
+    Observable.race(e1, e2).subscribe(x => {
+      expect(x).to.be.true;
+    }, done, done);
+  });
 });

src/operator/race.ts

@@ -82,15 +82,18 @@ export class RaceSubscriber<T> extends OuterSubscriber<T, T> {
   protected _complete() {
     const observables = this.observables;
     const len = observables.length;
+
     if (len === 0) {
       this.destination.complete();
     } else {
       for (let i = 0; i < len; i++) {
         let observable = observables[i];
         let subscription = subscribeToResult(this, observable, observable, i);
 
-        this.subscriptions.push(subscription);
-        this.add(subscription);
+        if (this.subscriptions) {
+          this.subscriptions.push(subscription);
+          this.add(subscription);
+        }
       }
       this.observables = null;
     }