BUG/MEDIUM: mux-h2: Don't forget to quit the send list on error reports

Similar to last fix, we need to quit the send list when reporting an
error via the send side.

This should be backported to 1.9.

src/mux_h2.c

@@ -617,6 +617,8 @@ static void __maybe_unused h2s_notify_send(struct h2s *h2s)
 		sw->events &= ~SUB_RETRY_SEND;
 		tasklet_wakeup(sw->task);
 		h2s->send_wait = NULL;
+		LIST_DEL(&h2s->list);
+		LIST_INIT(&h2s->list);
 	}
 }