RFC 9110 14.2 says an origin server MUST ignore a Range header field
with a range unit it does not understand. parse_range_header() accepts
only bytes=, so a request such as "Range: items=1-2" got a 416 instead
of the full response. The unit is now checked first, and only a bytes
range is parsed and answered with a 416 when it is invalid.
39c98d4671
