http: do not send `0\r\n\r\n` in TE HEAD responses

When replying to a HEAD request, do not attempt to send the trailers and
EOF sequence (`0\r\n\r\n`). The HEAD request MUST not have body.

Quote from RFC:

The presence of a message body in a response depends on both the
request method to which it is responding and the response status code
(Section 3.1.2).  Responses to the HEAD request method (Section 4.3.2
of [RFC7231]) never include a message body because the associated
response header fields (e.g., Transfer-Encoding, Content-Length,
etc.), if present, indicate only what their values would have been if
the request method had been GET (Section 4.3.1 of [RFC7231]).

fix #8361

Reviewed-By: Timothy J Fontaine <tjfontaine@gmail.com>