http-headers parser fails on whitespace-only lines

Describe the bug

http_headers skips empty lines but not whitespace-only ones. filter(None, data.splitlines()) keeps a line containing only spaces or tabs, and the parser then reads its first word:

first_word = line.split(maxsplit=1)[0]

which raises IndexError for that line. On the command line this becomes "http-headers parser could not parse the input data". curl_head has the same failure because it calls http_headers.parse.

To Reproduce

printf 'GET / HTTP/1.1\nHost: example.com\n \nAccept: */*\n' | jc --http-headers

jc:  Error - http-headers parser could not parse the input data. ...

import jc.parsers.http_headers as http_headers

http_headers.parse('GET / HTTP/1.1\nHost: example.com\n \nAccept: */*\n', quiet=True)
# IndexError: list index out of range

A response with a whitespace-only line fails the same way, and so does jc --curl-head for the same input.

Expected behavior

Whitespace-only lines are treated like the empty lines the parser already drops, so the surrounding request or response still parses. hosts got the same treatment in #742/#743.

Environment

• jc version: 1.26.0 (dev)
• Python version: 3.13