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(pdfManager, arg) {
    let stream;
    if (isStream(arg)) {
      stream = arg;
    } else if (isArrayBuffer(arg)) {
      stream = new Stream(arg);
    } else {
      throw new Error("PDFDocument: Unknown argument type");
    }
    if (stream.length <= 0) {
      throw new InvalidPDFException(
        "The PDF file is empty, i.e. its size is zero bytes."
      );
    }
    this.pdfManager = pdfManager;
    this.stream = stream;
    this.xref = new XRef(stream, pdfManager);
    this._pagePromises = [];
    this._version = null;
    const idCounters = {
      font: 0,
    };
    this._globalIdFactory = class {
      static getDocId() {