BUG/MEDIUM: stconn: Reset SE descriptor when we fail to create a stream

If stream_new() fails after the frontend SC is attached, the underlying SE
descriptor is not properly reset. Among other things, SE_FL_ORPHAN flag is
not set again. Because of this error, a BUG_ON() is triggered when the mux
stream on the frontend side is destroyed.

Thus, now, when stream_new() fails, SE_FL_ORPHAN flag is set on the SE
descriptor and its stream-connector is set to NULL.

This patch should solve the issue #1880. It must be backported to 2.6.
diff --git a/src/stconn.c b/src/stconn.c
index 36d19b4..3ad075f 100644
--- a/src/stconn.c
+++ b/src/stconn.c
@@ -170,7 +170,9 @@
 		return NULL;
 	if (unlikely(!stream_new(sess, sc, input))) {
 		pool_free(pool_head_connstream, sc);
-		sc = NULL;
+		sd->sc = NULL;
+		se_fl_set(sd, SE_FL_ORPHAN);
+		return NULL;
 	}
 	se_fl_clr(sd, SE_FL_ORPHAN);
 	return sc;