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):

scaleX = drawnWidth / MAX_GROUP_SIZE;
        drawnWidth = MAX_GROUP_SIZE;
      }
      if (drawnHeight > MAX_GROUP_SIZE) {
        scaleY = drawnHeight / MAX_GROUP_SIZE;
        drawnHeight = MAX_GROUP_SIZE;
      }
      let cacheId = "groupAt" + this.groupLevel;
      if (group.smask) {
        
        cacheId += "_smask_" + (this.smaskCounter++ % 2);
      }
      const scratchCanvas = this.cachedCanvases.getCanvas(
        cacheId,
        drawnWidth,
        drawnHeight,
        true
      );
      const groupCtx = scratchCanvas.context;
      
      
      groupCtx.scale(1 / scaleX, 1 / scaleY);
      groupCtx.translate(-offsetX, -offsetY);
      groupCtx.transform.apply(groupCtx, currentTransform);
      if (group.smask) {
        
        this.smaskStack.push({
          canvas: scratchCanvas.canvas,
          context: groupCtx,
          offsetX,