Use same lib instance in __init__ and __del__
Use same lib instance in __init__ and __del__

This fixes segfaults when running test_playlist.py on Python 3.4, since
__del__() is called after the spotify.lib patch is removed.

felix1m/pyspotify,jodal/pyspotify,jodal/pyspotify,kotamat/pyspotify,kotamat/pyspotify,mopidy/pyspotify,jodal/pyspotify,felix1m/pyspotify,mopidy/pyspotify,kotamat/pyspotify,felix1m/pyspotify