src: avoid returning invalid value from hex2bin
If the input is not a valid hexadecimal digit, hex2bin
should not return an invalid value, which is not handled correctly by the caller, which is the PercentDecode
function. However, PercentDecode
only ever calls the hex2bin
function with valid hexadecimal digits, so mark the code path that previously returned an invalid value for non-digits as UNREACHABLE
.