fix when checking video from live stream

[laxa]

Videos from live streams are not always working (this is an assumption), for example, with the develop branch, pip3 install --user youtube-dl and the following video https://www.youtube.com/watch?v=vsDknmK30C0, the following stacktrace is observed:

>>> import pafy
>>> pafy.new("https://www.youtube.com/watch?v=vsDknmK30C0")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/laxa/Documents/pafy/pafy/pafy.py", line 124, in new
    return Pafy(url, basic, gdata, size, callback, ydl_opts=ydl_opts)
  File "/home/laxa/Documents/pafy/pafy/backend_youtube_dl.py", line 31, in __init__
    super(YtdlPafy, self).__init__(*args, **kwargs)
  File "/home/laxa/Documents/pafy/pafy/backend_shared.py", line 97, in __init__
    self._fetch_basic()
  File "/home/laxa/Documents/pafy/pafy/backend_youtube_dl.py", line 53, in _fetch_basic
    self._author = self._ydl_info['uploader']
KeyError: 'uploader'

The following PR resolves this issue, the video is then playable inside mpsyt. This partially solves issue #193

[belgianguy]

I can attest that this fix was needed to be able to open a LiveStream (LabPadre SpaceX livestream) through pafy (using VidGear)
I got the exact same error that Laxa got, which was resolved (and the live stream showed up)