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):

c3 = tmp;
  }
  if (coords[p1 + 1] > coords[p2 + 1]) {
    tmp = p1;
    p1 = p2;
    p2 = tmp;
    tmp = c1;
    c1 = c2;
    c2 = tmp;
  }
  const x1 = (coords[p1] + context.offsetX) * context.scaleX;
  const y1 = (coords[p1 + 1] + context.offsetY) * context.scaleY;
  const x2 = (coords[p2] + context.offsetX) * context.scaleX;
  const y2 = (coords[p2 + 1] + context.offsetY) * context.scaleY;
  const x3 = (coords[p3] + context.offsetX) * context.scaleX;
  const y3 = (coords[p3 + 1] + context.offsetY) * context.scaleY;
  if (y1 >= y3) {
    return;
  }
  const c1r = colors[c1],
    c1g = colors[c1 + 1],
    c1b = colors[c1 + 2];
  const c2r = colors[c2],
    c2g = colors[c2 + 1],
    c2b = colors[c2 + 2];
  const c3r = colors[c3],
    c3g = colors[c3 + 1],
    c3b = colors[c3 + 2];
  const minY = Math.round(y1),
    maxY = Math.round(y3);