plugins/pay: don't crash if getroute is empty.

This can't happen because we go the self-pay path in this case, but
once we fix that for bolt12, this can be reached.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

plugins/libplugin-pay.c

@@ -954,6 +954,7 @@ static struct command_result *payment_getroute(struct payment *p)
 		payment_root(p)->abort = true;
 		payment_fail(p, "Empty route returned by getroute, are you "
 				"trying to pay yourself?");
+		return command_still_pending(p->cmd);
 	}
 
 	fee = payment_route_fee(p);