fix(animations): allow players to be destroyed before initialized (#13346)

Closes #13293
Closes #13346

modules/@angular/platform-browser/src/dom/web_animations_player.ts

@@ -124,7 +124,11 @@ export class WebAnimationsPlayer implements AnimationPlayer {
     this._started = false;
   }
 
-  private _resetDomPlayerState() { this._player.cancel(); }
+  private _resetDomPlayerState() {
+    if (this._player) {
+      this._player.cancel();
+    }
+  }
 
   restart(): void {
     this.reset();

modules/@angular/platform-browser/test/dom/web_animations_player_spec.ts

@@ -175,6 +175,12 @@ export function main() {
       expect(data['keyframes']).toEqual([{opacity: '0.5'}, {opacity: '1'}]);
     });
 
+    it('should allow the player to be destroyed before it is initialized', () => {
+      const elm = el('<div></div>');
+      const player = new ExtendedWebAnimationsPlayer(elm, [], {});
+      expect(() => { player.destroy(); }).not.toThrowError();
+    });
+
     describe('previousStyle', () => {
       it('should merge keyframe styles based on the previous styles passed in when the player has finished its operation',
          () => {