Mainloop lock needs to be held to access PulseAudio object from outside the
event loop thread, in particular in GetPosition() calls. Otherwise we might hit
a race condition and have the call fail. There's also a possibility that the
call might randomly fail if it's called before first timing data is received
for the stream, so handle that case as well.
Also fix the stream write callback to call Mix() with correct parameters, as
well as do the work in a loop in case pa_stream_begin_write() returns smaller
memory buffer than was requested.
phantom10111
b365dcd65d