BUG/MINOR: log: t_idle (%Ti) is not set for some requests

If TCP content inspection is used, msg_state can be >= HTTP_MSG_ERROR
the first time http_wait_for_request is called. t_idle was being left
unset in that case.

In the example below :
     stick-table type string len 64 size 100k expire 60s
     tcp-request inspect-delay 1s
     tcp-request content track-sc1 hdr(X-Session)

%Ti will always be -1, because the msg_state is already at HTTP_MSG_BODY
when http_wait_for_request is called for the first time.

This patch should backported to 1.8 and 1.7.
diff --git a/src/proto_http.c b/src/proto_http.c
index 8370889..6730375 100644
--- a/src/proto_http.c
+++ b/src/proto_http.c
@@ -1619,18 +1619,16 @@
 	/* we're speaking HTTP here, so let's speak HTTP to the client */
 	s->srv_error = http_return_srv_error;
 
+	/* If there is data available for analysis, log the end of the idle time. */
+	if (buffer_not_empty(req->buf) && s->logs.t_idle == -1)
+		s->logs.t_idle = tv_ms_elapsed(&s->logs.tv_accept, &now) - s->logs.t_handshake;
+
 	/* There's a protected area at the end of the buffer for rewriting
 	 * purposes. We don't want to start to parse the request if the
 	 * protected area is affected, because we may have to move processed
 	 * data later, which is much more complicated.
 	 */
 	if (buffer_not_empty(req->buf) && msg->msg_state < HTTP_MSG_ERROR) {
-
-		/* This point is executed when some data is avalaible for analysis,
-		 * so we log the end of the idle time. */
-		if (s->logs.t_idle == -1)
-			s->logs.t_idle = tv_ms_elapsed(&s->logs.tv_accept, &now) - s->logs.t_handshake;
-
 		if (txn->flags & TX_NOT_FIRST) {
 			if (unlikely(!channel_is_rewritable(req))) {
 				if (req->flags & (CF_SHUTW|CF_SHUTW_NOW|CF_WRITE_ERROR|CF_WRITE_TIMEOUT))