fixing disabled line wrapping for HTML

This pull request fixes issue #342

This is also an alternative to the pull request https://github.com/einars/js-beautify/pull/423, added to maintain backwards compatibility and more complete tests (string and number values).

The check in that pull request states within it that when `wrap_line_length` and `max_char` are undefined, set `wrap_line_length` to undefined (even though it already is).  This loses the backwards compatibility with 1.3.4 where `max_char` overwrote `wrap_line_length` if it was 0 or undefined.

This issue started because the conditional updated in commit https://github.com/einars/js-beautify/commit/132fc95e9090afa4f9de1ff4f25c64b5e3f878bc, although more complete (checking undefined and 0), reversed the logic from `!== undefined` to `=== undefined`.