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):

let prefs = null;
    if (isDict(obj)) {
      for (const key in ViewerPreferencesValidators) {
        if (!obj.has(key)) {
          continue;
        }
        const value = obj.get(key);
        
        if (!ViewerPreferencesValidators[key](value)) {
          info(`Bad value in ViewerPreferences for "${key}".`);
          continue;
        }
        let prefValue;
        switch (key) {
          case "NonFullScreenPageMode":
            switch (value.name) {
              case "UseNone":
              case "UseOutlines":
              case "UseThumbs":
              case "UseOC":
                prefValue = value.name;
                break;
              default:
                prefValue = "UseNone";
            }
            break;
          case "Direction":
            switch (value.name) {
              case "L2R":
              case "R2L":