libwebsockets

cgi: fix killing cgi before draining its output

CGI's which don't have content-length nor they are explicitly chunked
are killed immediately after being reaped even if their output has not
being drained. This is fixed by deferring from killing them like those
which are explicitly chunked.

Signed-off-by: Petar Paradzik <petar.paradzik@sartura.hr>