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
pdfFonts.push(font);
      },
      clone() {
        return this;
      },
    };
    const fonts = new Map();
    fontRes.forEach((fontName, font) => {
      fonts.set(fontName, font);
    });
    const promises = [];
    for (const [fontName, font] of fonts) {
      const descriptor = font.get("FontDescriptor");
      if (!(descriptor instanceof Dict)) {
        continue;
      }
      let fontFamily = descriptor.get("FontFamily");
      
      fontFamily = fontFamily.replace(/[ ]+([0-9])/g, "$1");
      const fontWeight = descriptor.get("FontWeight");
      
      
      
      const italicAngle = -descriptor.get("ItalicAngle");
      const cssFontInfo = { fontFamily, fontWeight, italicAngle };
      if (!validateCSSFont(cssFontInfo)) {
        continue;
      }
      promises.push(