bad error if parenthetical inside rule

https://www.puzzlescript.net/editor.html?hack=daad222319fd2295732de7a5bf8b9568

```
[ > Player | Crate (hello) ] -> [ > Player | > Crate ] 
```

produces errors

line 78 : A rule has to have an arrow in it. There's no arrow here! Consider reading up about rules - you're clearly doing something weird
line 78 : This rule refers to nothing. What the heck? :O