Fuzz: do proper division for negative values
Fuzz: do proper division for negative values

When vs > 0 and image is too short there might occur intermediate negative value.
Right shift is incorrect for that value and implementation-defined for signed
type.
Just do integer division instead and hope compiler will turn it to arithmetic shift.
libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl