MINOR: proto-htx: Use channel_htx_fwd_all() when unfiltered body are forwarded

So the first block position of the HTX message will always be updated
accordingly.
diff --git a/src/proto_htx.c b/src/proto_htx.c
index 7cc26ba..f596294 100644
--- a/src/proto_htx.c
+++ b/src/proto_htx.c
@@ -1225,7 +1225,7 @@
 			goto missing_data_or_waiting;
 	}
 	else {
-		c_adv(req, htx->data - co_data(req));
+		channel_htx_fwd_all(req, htx);
 		if (msg->flags & HTTP_MSGF_XFER_LEN)
 			channel_htx_forward_forever(req, htx);
 	}
@@ -2222,7 +2222,7 @@
 			goto missing_data_or_waiting;
 	}
 	else {
-		c_adv(res, htx->data - co_data(res));
+		channel_htx_fwd_all(res, htx);
 		if (msg->flags & HTTP_MSGF_XFER_LEN)
 			channel_htx_forward_forever(res, htx);
 	}