BUG/MEDIUM: h1-htx: Properly handle bodyless messages

BUG/MEDIUM: h1-htx: Properly handle bodyless messages

During h1 parsing, there are some postparsing checks to detect bodyless
messages and switch the parsing in DONE state. However, a case was not
properly handled. Responses to HEAD requests with a "transfer-encoding"
header. The response parser remained blocked waiting for the response body.

To fix the issue, the postparsing was sliglty modified. Instead of trying to
handle bodyless messages in a common way between the request and the
response, it is now performed in the dedicated postparsing functions. It is
easier to enumerate all cases, especially because there is already a test
for responses to HEAD requests.

This patch should fix the issue #2836. It must be backported as far as 2.9.