Prefer Microsoft encodings to Mac encodings

Fixes <a href="https://bugzilla.mozilla.org/show_bug.cgi?id=833676">bug 833676</a>.
According to PDF Reference 9.6.6.4, Microsoft encodings should have higher precedence than Mac encodings. And Mac encodings actually tend to have bogus values because format 0 subtable can't represent glyphID larger than 255.