BUG/MEDIUM: http-client: Notify applet has more data to deliver until the EOM

BUG/MEDIUM: http-client: Notify applet has more data to deliver until the EOM

When we leave the I/O handler with an unfinished request, we must report the
applet has more data to deliver. Otherwise, when the channel request buffer
is emptied, the http-client applet is not always woken up to forward the
remaining request data.

This issue was probably revealed by commit "BUG/MEDIUM: http-client: Don't
wake http-client applet if nothing was xferred". It is only an issue with
large POSTs, when the payload is streamed.

This patch must be backported as far as 2.6 with the commit above. But on
older versions, the applet API may differ. So be careful.

(cherry picked from commit 0b97bf36fad6fbced8077ac416a1399c05806c7d)
Signed-off-by: Amaury Denoyelle <adenoyelle@haproxy.com>
(cherry picked from commit dd3ba78fc13a99e79052496d1851cff65c24f73c)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>