Missing braces in condition

It will try to play the file _even_ if it failed to download it.

Thanks to @neophob for [reporting it](https://github.com/jishi/node-sonos-http-api/commit/1c45478de1d71558825770e985eff24d958a27b6#commitcomment-8565662).
Merge pull request #30 from matiasgarciaisaia/patch-1

Missing braces in condition