* Only issue matching token errors on non-dupe locations
Intead of unconditionally retrieving the last error and attaching a
related span, `parseErrorAt` and friends now return the last error and
return `false` when there is none.
Also make one more place use parseExpectedMatchingBrackets that I missed
last time.
* Inline parseTokenForError, return undefined not false
* skip redundant undefined assignment
* address PR comments