Fix grammar proxy issue
Fix grammar proxy issue

It is possible to have GrammarProxy in the rule list. This is the case
when doing something like this:
  A = token("...")
  B = field("A", A)

lcheylus/haka,Wingless-Archangel/haka,haka-security/haka,LubyRuffy/haka,nabilbendafi/haka,haka-security/haka,nabilbendafi/haka,Wingless-Archangel/haka,lcheylus/haka,lcheylus/haka,LubyRuffy/haka,nabilbendafi/haka,haka-security/haka