Attach (recommended) or Link to PDF file here:  [test.pdf](https://akmer.aikucun.com/a94a8fe5ccb19ba61c4c0873d391e987982fbbd3_1616477914120_83.pdf)


Configuration:
- Web browser and its version: chrome 87.0.4280.88
- Operating system and its version: windows10
- PDF.js version: 2.6.347
- Is a browser extension:

Steps to reproduce the problem:
1. just open 

What is the expected behavior? (add screenshot)

What went wrong? (add screenshot)
![image](https://user-images.githubusercontent.com/17724610/112087066-473f8f80-8bc8-11eb-8efb-56139ec42a9c.png)

Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension):

case "A":
        case "a":
          const LIMIT = 26; 
          const A_UPPER_CASE = 0x41,
            A_LOWER_CASE = 0x61;
          const baseCharCode = style === "a" ? A_LOWER_CASE : A_UPPER_CASE;
          const letterIndex = currentIndex - 1;
          const character = String.fromCharCode(
            baseCharCode + (letterIndex % LIMIT)
          );
          const charBuf = [];
          for (let j = 0, jj = (letterIndex / LIMIT) | 0; j <= jj; j++) {
            charBuf.push(character);
          }
          currentLabel = charBuf.join("");
          break;
        default:
          if (style) {
            throw new FormatError(
              `Invalid style "${style}" in PageLabel dictionary.`
            );
          }
          currentLabel = "";
      }
      pageLabels[i] = prefix + currentLabel;
      currentIndex++;
    }
    return pageLabels;
  }
  get pageLayout() {