Patching a range bug in nesf-live-whitespace-at-point-p.

It throws an error if the point is at the end of the file, so calling `cider-eval-expression-at-point` throws an error if the expression is the last thing in the file (with no trailing whitespace).

Whilst this patch works, I'm not 100% sure this is the best way to fix it, because now the comment string isn't strictly true - it's testing for whitespace or end-of-file. But I'm not sure it's worth spinning out into a separate predicate & test. Up to you...

(Oh, one small nice thing about using `char-syntax` instead of `string-match` is that it respects the current mode's syntax table's definition of whitespace.)