Handle empty 'fmt_list' or 'url_encoded_fmt_stream_map' on live streams

Hi,
It looks like this breaks when calling getInfo on a YouTube live stream. 

The info object returned has fmt_list and url_encoded_fmt_stream_map as empty strings, which throws an error when map is called. 

I've wrapped these calls in a conditional:
````
    if (info.fmt_list) {
      info.fmt_list = info.fmt_list.map(function(format) {
        return format.split('/');
      });
    } else {
      info.fmt_list = [];
    }
````
Info object: https://gist.github.com/liuhenry/5528941