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
const fontName = normalizeFontName(name);
  const fontMap = getXFAFontMap();
  return fontMap[fontName];
}
function getXfaFontWidths(name) {
  const info = getXfaFontName(name);
  if (!info) {
    return null;
  }
  const { baseWidths, factors } = info;
  if (!factors) {
    return baseWidths;
  }
  return baseWidths.map((w, i) => w * factors[i]);
}
export { getXfaFontName, getXfaFontWidths };