Attach (recommended) or Link to PDF file here:
[backgroundimage_not_visible_anonymisiert.pdf](https://github.com/mozilla/pdf.js/files/6544725/backgroundimage_not_visible_anonymisiert.pdf)


Configuration:
- Web browser and its version: Chrome Version 90.0.4430.212 (Offizieller Build) (x86_64)
- Operating system and its version: Windows 10, MacOs BigSur
- PDF.js version: 2.5.207
- Is a browser extension: no

Steps to reproduce the problem:
1. open the document in demo viewer.js
2.

What is the expected behavior? (add screenshot)
The backgroundimage gets rendered like in Acrobat Reader
<img width="1348" alt="Bildschirmfoto 2021-05-26 um 09 44 21" src="https://user-images.githubusercontent.com/1286150/119621970-00a82480-be07-11eb-8fed-f74ac04b840b.png">

What went wrong? (add screenshot)
Backgroundimage is not rendered only some  text
<img width="987" alt="Bildschirmfoto 2021-05-26 um 09 43 57" src="https://user-images.githubusercontent.com/1286150/119621938-fab24380-be06-11eb-92ac-4ecb2c9334b1.png">




Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension):

const ps = figure.coords;
  const cs = figure.colors;
  let i, ii;
  switch (figure.type) {
    case "lattice":
      const verticesPerRow = figure.verticesPerRow;
      const rows = Math.floor(ps.length / verticesPerRow) - 1;
      const cols = verticesPerRow - 1;
      for (i = 0; i < rows; i++) {
        let q = i * verticesPerRow;
        for (let j = 0; j < cols; j++, q++) {
          drawTriangle(
            data,
            context,
            ps[q],
            ps[q + 1],
            ps[q + verticesPerRow],
            cs[q],
            cs[q + 1],
            cs[q + verticesPerRow]
          );
          drawTriangle(
            data,