Portaudio Mono

* Observed on OS X, fldigi cannot work on audio cards with mono output
    - it requests 2 channels from PortAudio no matter what and portaudio
      will complain if the audio output is only mono.
    - modified SoundPort::init_stream to make sure that if max_channels < 2
      sd[1].params.channelCount is updated to max_channels

src/soundcard/sound.cxx

@@ -1602,6 +1602,8 @@ void SoundPort::init_stream(unsigned dir)
 				else
 						sd[1].params.suggestedLatency = (*sd[dir].idev)->defaultHighOutputLatency;
 		sd[1].params.hostApiSpecificStreamInfo = NULL;
+		if (max_channels < 2)
+			sd[1].params.channelCount = max_channels;
 	}
 
 	const vector<double>& rates = supported_rates[dir][(*sd[dir].idev)->name];