Attach (recommended) or Link to PDF file here:
[FormDB2_fr.pdf](https://github.com/mozilla/pdf.js/files/7352426/FormDB2_fr.pdf)

Configuration:
- Web browser and its version: Firefox nightly
- Operating system and its version: linux debian

Steps to reproduce the problem:
1. Open the pdf
2. The image on the top of each pages is missing 

What is the expected behavior? (add screenshot)
![image](https://user-images.githubusercontent.com/5641725/137465500-e8788893-f33d-4532-871d-43b464fa85f4.png)

What went wrong? (add screenshot)
![image](https://user-images.githubusercontent.com/5641725/137465363-f2b35fe4-6776-45e9-b9e4-ccef6d9ad670.png)

return this.contentType === "text/html";
  }
  [$onChild](child) {
    if (
      this.contentType === "text/html" &&
      child[$namespaceId] === NamespaceIds.xhtml.id
    ) {
      this[$content] = child;
      return true;
    }
    if (this.contentType === "text/xml") {
      this[$content] = child;
      return true;
    }
    return false;
  }
  [$toHTML](availableSpace) {
    if (this.contentType !== "text/html" || !this[$content]) {
      
      return HTMLResult.EMPTY;
    }
    return this[$content][$toHTML](availableSpace);
  }
}
class ExObject extends XFAObject {