cjxl: improve quality to distance calculation (#1743)
cjxl: improve quality to distance calculation (#1743)

We change a detail in the calculation going from quality to distance:
now it is continous near the value 30, corresponding to distance 6.4.
libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl