js2-forward-sexp doesn't work when the buffer is narrowed.

[milkypostman]

parse-partial-sexp is getting called with a range that is outside of the narrowed buffer and this causes problems. I'm not sure what the fix is because I don't have a ton of experience w/ this codebase.

this is with the latest head version.

[dgutov]

We do a widen before maybe parsing the buffer, in order to counteract narrowing by blink-matching-open (#63).
Maybe we should just extend this save-restriction block to the whole function body.

[dgutov]

That seems to do it.