Xpra: Ticket #45: avoid client error due to missing pulseaudio X11 props

Missing window or missing property or wrong property type PULSE_SERVER (latin1)
Traceback (most recent call last):
   File "/usr/lib/python2.7/dist-packages/wimpiggy/prop.py", line 277, in prop_get
     data = trap.call_synced(XGetWindowProperty, target, key, atom)
   File "/usr/lib/python2.7/dist-packages/wimpiggy/error.py", line 101, in call_synced
     return self._call(False, fun, args, kwargs)
   File "/usr/lib/python2.7/dist-packages/wimpiggy/error.py", line 86, in _call
     value = fun(*args, **kwargs)
   File "bindings.pyx", line 484, in wimpiggy.lowlevel.bindings.XGetWindowProperty (wimpiggy/lowlevel/bindings.c:4189)
 NoSuchProperty: PULSE_SERVER

and also for PULSE_COOKIE and PULSE_ID

Also, should the property name be using latin1?