BUG/MEDIUM: filters: Forward all filtered data at the end of http filtering

BUG/MEDIUM: filters: Forward all filtered data at the end of http filtering

When http filtering ends, if there are some filtered data not forwarded yet, we
forward them, in flt_http_end(). Most of time, this doesn't happen, except when
a tunnel is established using a CONNECT. In this case, there is not EOM on the
request and there is no body. Thus the headers are never forwarded, blocking the
stream.

This patch must be backported as far as 2.0. Prior versions don't suffer of this
bug because there is no HTX support. On the 2.0, the change is only applicable
on HTX streams. A special test must be performed to make sure.

(cherry picked from commit 22fca1f2c84334096e38d78ffc674be19c3e0292)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>