Error in getting frames of IR stream with 320*240 @30fps

[Victor]

@smoli You may need to set the IR mode first

astra::ImageStreamMode irMode;
irMode.set_width(640);
irMode.set_height(480);
irMode.set_pixel_format(astra_pixel_formats::ASTRA_PIXEL_FORMAT_GRAY16);
irMode.set_fps(30);
irStream.set_mode(irMode);