This permits the following to work to convert an RGB image to
16bit integer tiff with the desired ICC profile:

gegl input.jpg -- convert-space path=FOGRA29L_uncoated.icc tiff-save path=output.tif bitdepth=16 fp=0

This will also work for a file loaded with a CMYK ICC profile that has been
"demoted" to RGB at some point in the chain.