Fixes to work on OSX

[virtuald]

• Loads appropriate pulseaudio dylib
• Fixes the following bug

$ ./pulsemixer 
Traceback (most recent call last):
  File "./pulsemixer", line 2057, in <module>
    main()
  File "./pulsemixer", line 1951, in main
    curses.wrapper(Screen(CFG.ui.color, CFG.ui.mouse).run)
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/curses/__init__.py", line 94, in wrapper
    return func(stdscr, *args, **kwds)
  File "./pulsemixer", line 1292, in run
    self.change_mode(2)
  File "./pulsemixer", line 1146, in change_mode
    self.get_data()
  File "./pulsemixer", line 1458, in get_data
    self.data = self.build(self.modes_data[2][0], PULSE.card_list(), [])
  File "./pulsemixer", line 1421, in build
    bar = Bar(s[0])
  File "./pulsemixer", line 943, in __init__
    self.fullname = pa.description.decode()
AttributeError: 'NoneType' object has no attribute 'decode'

pulseaudio version (installed via homebrew):

$ pulseaudio --version
W: [] caps.c: Normally all extra capabilities would be dropped now, but that's impossible because PulseAudio was built without capabilities support.
pulseaudio 13.0

[sotpapathe]

Can't see anything wrong with the changes and it still works on Linux. Can't test it on OSX though.