Cast Extension: Loading an item without starting playback

### Issue description
This issue happens only with Cast Extension.

I want to load an item without starting playback automatically, it should only start if user clicks play button. By default when i load an item the playback starts automatically.

I tried to set "PlayWhenReady" to false before load, but it played the video anyway.

### Reproduction steps
Connect to Chromecast sending a video URL with loadItem method.

### Link to test content
https://www.skillscommons.org/bitstream/handle/taaccct/10109/Operational%20Amplifiers%20(1).mp4

But it happens with any URL i tested.

### Version of ExoPlayer being used
2.7.0

### Device(s) and version(s) of Android being used
Google Pixel 2 XL, Android 8.1.0 and a Chromecast connected to my TV.

### A full bug report captured from the device
I don't get any exception message.