SoundCloud player doesn't get destroyed if you're quick like a QA engineer

[Fauntleroy]

If you switch to another media URL before the SoundCloud SDK loads an initializes, the SoundCloud player will stay alive... forever. I imagine this is because this.stop() does nothing when this.player doesn't exist yet.

To replicate:

• npm run start
• Go to http://localhost:3000/
• Very quickly click "Soundcloud song" then "Vimeo video"
• The Soundcloud song will continue playing while the Vimeo video plays

This should never happen in the wild, so I don't think it's a high priority at this time.

[cookpete]

Good spot. Should be easy enough to fix, we could either:

• Around here just check this.isMounted() and bail if not.
• Assign any data requests to local properties and abort them on componentWillUnmount

[cookpete]

Will probably have to use this.isMounted(), as it looks like load-script (used to load the SDK) doesn't have an abort function.

[cookpete]

Actually this.isMounted() wasn't enough. I've added a fix that checks the url we originally intended to load against the current props.url after the various requests are done, and aborts streaming if they differ.