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
constructor(pdfFonts) {
    this.fonts = new Map();
    this.cache = new Map();
    this.warned = new Set();
    this.defaultFont = null;
    this.add(pdfFonts);
  }
  add(pdfFonts) {
    for (const pdfFont of pdfFonts) {
      this.addPdfFont(pdfFont);
    }
    for (const pdfFont of this.fonts.values()) {
      if (!pdfFont.regular) {
        pdfFont.regular = pdfFont.italic || pdfFont.bold || pdfFont.bolditalic;
      }
    }
  }
  addPdfFont(pdfFont) {
    const cssFontInfo = pdfFont.cssFontInfo;
    const name = cssFontInfo.fontFamily;
    let font = this.fonts.get(name);
    if (!font) {
      font = Object.create(null);
      this.fonts.set(name, font);
      if (!this.defaultFont) {
        this.defaultFont = font;
      }
    }
    let property = "";
    if (cssFontInfo.italicAngle !== "0") {