win-dshow: Fix video playback when default format is MJPEG

Video playback doesn't work if the default format is MJPEG and there are
other formats to use; this is because the useDefaultConfig variable is
still set to true, which overrides the format value that would normally
tell it to convert to RGB.

plugins/win-dshow/win-dshow.cpp

@@ -847,6 +847,8 @@ bool DShowInput::UpdateVideoConfig(obs_data_t *settings)
 
 	if (videoConfig.internalFormat == VideoFormat::MJPEG) {
 		videoConfig.format = VideoFormat::XRGB;
+		videoConfig.useDefaultConfig = false;
+
 		if (!device.SetVideoConfig(&videoConfig)) {
 			blog(LOG_WARNING, "%s: device.SetVideoConfig (XRGB) "
 					"failed", obs_source_get_name(source));