Re-enable trust sigils on Restart Session.

In my eagerness to make sure we didn't _accidentally_ change the
seat's trust status back to trusted at any point, I forgot to do it on
purpose if a second SSH login phase is legitimately run in the same
terminal after the first session has ended.

windows/window.c

@@ -385,6 +385,7 @@ static void start_backend(void)
 	cleanup_exit(1);
     }
 
+    seat_set_trust_status(win_seat, true);
     error = backend_init(vt, win_seat, &backend, logctx, conf,
                          conf_get_str(conf, CONF_host),
                          conf_get_int(conf, CONF_port),