WDM-KS: don't request a zero buffer size

This fixes an issue where Pa_OpenStream() would fail on WDM-KS WinRT
devices if suggestedLatency is zero.

Fixes #761

src/hostapi/wdmks/pa_win_wdmks.c

@@ -4734,6 +4734,10 @@ static PaError OpenStream( struct PaUtilHostApiRepresentation *hostApi,
         {
             stream->capture.framesPerBuffer = stream->capture.pPin->frameSize;
         }
+        else if(stream->capture.framesPerBuffer == 0) {
+            /* WinRT devices will reject a zero RequestedBufferSize. See https://github.com/PortAudio/portaudio/issues/761 */
+            stream->capture.framesPerBuffer = 1;
+        }
         PA_DEBUG(("Input frames chosen:%ld\n",stream->capture.framesPerBuffer));
 
         /* Setup number of packets to use */
@@ -4763,6 +4767,10 @@ static PaError OpenStream( struct PaUtilHostApiRepresentation *hostApi,
         {
             stream->render.framesPerBuffer = stream->render.pPin->frameSize;
         }
+        else if(stream->render.framesPerBuffer == 0) {
+            /* WinRT devices will reject a zero RequestedBufferSize. See https://github.com/PortAudio/portaudio/issues/761 */
+            stream->render.framesPerBuffer = 1;
+        }
         PA_DEBUG(("Output frames chosen:%ld\n",stream->render.framesPerBuffer));
 
         /* Setup number of packets to use */