BUG/MINOR: mux-h1: Fix condition to send null-chunk for bodyless message

BUG/MINOR: mux-h1: Fix condition to send null-chunk for bodyless message

When the EOH block is processed, before sending message headers, there is a
test to know if there is no payload. In case of a chunked message, a
null-chunk is emitted, except for bodyless response. For instance, a
response to a HEAD request has no payload at all and no null-chunk.

However, the test for bodyless responses is not correct. Only
H1S_F_BODYLESS_RESP flag is tested. But this flag can be set on server side
when we are processing the request. To fix the issue, the test was
adapted. The null-chunk is added if a message with no payload is chunked and
it is a request or a non-bodyless responses.

This patch must be backported to all stable version.