BUG/MEDIUM: h2: Don't wait for flow control if the connection had a shutr.

In h2_snd_buf(), if we couldn't send the data because of flow control, and
the connection got a shutr, then add CS_FL_ERROR (or CS_FL_ERR_PENDING). We
will never get any window update, so we will never be unlocked, anyway.

No backport is needed.
diff --git a/src/mux_h2.c b/src/mux_h2.c
index faa5d0b..0b28c38 100644
--- a/src/mux_h2.c
+++ b/src/mux_h2.c
@@ -4865,6 +4865,18 @@
 			tasklet_wakeup(h2s->h2c->wait_event.task);
 
 	}
+	/* If we're waiting for flow control, and we got a shutr on the
+	 * connection, we will never be unlocked, so add an error on
+	 * the conn_stream.
+	 */
+	if (conn_xprt_read0_pending(h2s->h2c->conn) &&
+	    !b_data(&h2s->h2c->dbuf) &&
+	    (h2s->flags & (H2_SF_BLK_SFCTL | H2_SF_BLK_MFCTL))) {
+		if (cs->flags & CS_FL_EOS)
+			cs->flags |= CS_FL_ERROR;
+		else
+			cs->flags |= CS_FL_ERR_PENDING;
+	}
 	return total;
 }