Only make `jpeg_transcode` set `butteraugli_distance` to 0 after it itself receives its correct value
Only make `jpeg_transcode` set `butteraugli_distance` to 0 after it itself receives its correct value

This fixes a recent breakage in the handling of `--distance`.

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