Don't decode the jbrd box when recon not requested
Don't decode the jbrd box when recon not requested

When no jpeg reconstruction is requested, there's no reason to parse the
box. This has no visible effect, at least at this time because currently
it can only output a reconstructed JPEG if both the reconstruction event
and the full image event were requested.

libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl