https://github.com/mozilla/pdf.js/issues/6397#issuecomment-164954332 Would have been a lot easier to find had there been an assertion checking that string16 didn't go out of bounds of the 16bit number.

originalCharCode,
    fontChar,
    unicode,
    accent,
    width,
    vmetric,
    operatorListId,
    isSpace,
    isInFont
  ) {
    return (
      this.originalCharCode === originalCharCode &&
      this.fontChar === fontChar &&
      this.unicode === unicode &&
      this.accent === accent &&
      this.width === width &&
      this.vmetric === vmetric &&
      this.operatorListId === operatorListId &&
      this.isSpace === isSpace &&
      this.isInFont === isInFont
    );
  }
}
function int16(b0, b1) {
  return (b0 << 8) + b1;
}
function writeSignedInt16(bytes, index, value) {