BUG/MEDIUM: h1: Don't try to subscribe if we had a connection error.

If the CO_FL_ERROR flag is set, and we weren't connected yet, don't attempt
to subscribe, as the underlying xprt may already have been destroyed.
diff --git a/src/mux_h1.c b/src/mux_h1.c
index c9c8f84..ae9e8fd 100644
--- a/src/mux_h1.c
+++ b/src/mux_h1.c
@@ -1794,7 +1794,7 @@
 	if (h1c->wait_event.events & SUB_RETRY_RECV)
 		return (b_data(&h1c->ibuf));
 
-	if (h1c->flags & H1C_F_CS_WAIT_CONN) {
+	if (!(conn->flags & CO_FL_ERROR) && h1c->flags & H1C_F_CS_WAIT_CONN) {
 		conn->xprt->subscribe(conn, conn->xprt_ctx, SUB_RETRY_RECV, &h1c->wait_event);
 		return 0;
 	}