fix(youtube-player): YT.Player is not a constructor (#20616)

* fix(youtube-player): YT.Player is not a constructor

fixes a race condition where window.YT would be truthy
but window.YT.Player would not be ready.

Fixes #20598

* fix(youtube-player): YT.Player is not a constructor test

added a test to prevent reggression, the test mimics a possible state
of
the YT object when loading, when window.YT exists but window.YT.Player
does not.

Fixes #20598

src/youtube-player/youtube-player.spec.ts

@@ -6,6 +6,7 @@ import {createFakeYtNamespace} from './fake-youtube-player';
 import {Subscription} from 'rxjs';
 
 const VIDEO_ID = 'a12345';
+const YT_LOADING_STATE_MOCK = {loading: 1, loaded: 0};
 
 describe('YoutubePlayer', () => {
   let playerCtorSpy: jasmine.Spy;
@@ -381,6 +382,8 @@ describe('YoutubePlayer', () => {
     });
 
     it('waits until the api is ready before initializing', () => {
+      (window.YT as any) = YT_LOADING_STATE_MOCK;
+
       fixture = TestBed.createComponent(TestApp);
       testComponent = fixture.debugElement.componentInstance;
       fixture.detectChanges();

src/youtube-player/youtube-player.ts

@@ -210,7 +210,7 @@ export class YouTubePlayer implements AfterViewInit, OnDestroy, OnInit {
     }
 
     let iframeApiAvailableObs: Observable<boolean> = observableOf(true);
-    if (!window.YT) {
+    if (!window.YT || !window.YT.Player) {
       if (this.showBeforeIframeApiLoads && (typeof ngDevMode === 'undefined' || ngDevMode)) {
         throw new Error('Namespace YT not found, cannot construct embedded youtube player. ' +
             'Please install the YouTube Player API Reference for iframe Embeds: ' +