Player.destroy() throws exception when Audio is disabled.

When calling Player.destroy() on a player with the `audio: false` setting an exception is thrown:
```js
Uncaught TypeError: Cannot read property 'destroy' of undefined
    at Player.destroy (jsmpeg.min.js:formatted:264)
```

It appears that because `audio: false` is used, `this.audioOut` is undefined and therefore `this.audioOut.destroy()` fails when called in `Player.prototype.destroy()`.