Attach (recommended) or Link to PDF file here:
http://help.adobe.com/en_US/livecycle/11.0/SampleForms/941/Form.pdf

- Web browser and its version: Firefox 89.0.1
- Operating system and its version: Windows 10 10.0.19043.1052
- PDF.js version: commit bdfcdd6f8326f22c135edfa29a341ea4c558f3d1
- Is a browser extension: No

Steps to reproduce the problem:
1. Enable XFA support
2. Open form

What is the expected behavior? (add screenshot)
Page 3 (of 4) renders
![image](https://user-images.githubusercontent.com/7104454/122686842-622e9980-d1e1-11eb-92ab-86fe488560f2.png)

What went wrong? (add screenshot)
Only 3 pages total render in pdf.js
return this.dims[pageIndex];
  }
  get numberPages() {
    if (!this.pages) {
      this._createPages();
    }
    return this.dims.length;
  }
  setImages(images) {
    this.form[$globalData].images = images;
  }
  setFonts(fonts) {
    this.form[$globalData].fontFinder = new FontFinder(fonts);
    const missingFonts = [];
    for (let typeface of this.form[$globalData].usedTypefaces) {
      typeface = stripQuotes(typeface);
      const font = this.form[$globalData].fontFinder.find(typeface);
      if (!font) {
        missingFonts.push(typeface);
      }
    }
    if (missingFonts.length > 0) {
      return missingFonts;
    }
    return null;
  }
  appendFonts(fonts) {