Report thread running so Pa_StartStream can return prior to PaStreamCallback

Report thread running so Pa_StartStream can return prior to PaStreamCallback

StartStream() calls WaitForSingleObject(stream->hThreadStart, 60*1000)
but it will not be able to return until X number of PaStreamCallback
have been performed by ProcessOutputBuffer().

The above behaviour will cause a deadlock if the user supplied
PaStreamCallback tries to access a shared lock currently held by the
function calling Pa_StartStream().

Also it's a bit weird that you start receiving PaStreamCallbacks
before Pa_StartStream() is able to complete.