Viewer:  https://mozilla.github.io/pdf.js/web/viewer.html
Chrome on Windows 10
When the attached PDF file is viewed, some of the fonts display as garbled text. 
[Arial, Courier, Times New Roman]
The file views correctly in Adobe Reader.
[fff.pdf](https://github.com/mozilla/pdf.js/files/4652174/fff.pdf)

if (privateUseAreaIndex >= PRIVATE_USE_AREAS.length) {
        warn("Ran out of space in font private use area.");
        break;
      }
      nextAvailableFontCharCode = PRIVATE_USE_AREAS[privateUseAreaIndex][0];
      privateUseOffetEnd = PRIVATE_USE_AREAS[privateUseAreaIndex][1];
    }
    const fontCharCode = nextAvailableFontCharCode++;
    if (glyphId === 0) {
      glyphId = newGlyphZeroId;
    }
    newMap[fontCharCode] = glyphId;
    toFontChar[originalCharCode] = fontCharCode;
  }
  return {
    toFontChar,
    charCodeToGlyphId: newMap,
    nextAvailableFontCharCode,
  };
}
function getRanges(glyphs, numGlyphs) {
  
  
  const codes = [];
  for (const charCode in glyphs) {
    
    if (glyphs[charCode] >= numGlyphs) {
      continue;
    }
    codes.push({ fontCharCode: charCode | 0, glyphId: glyphs[charCode] });