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):

if (width < measuredWidth && this.isFontSubpixelAAEnabled) {
            const characterScaleX = width / measuredWidth;
            restoreNeeded = true;
            ctx.save();
            ctx.scale(characterScaleX, 1);
            scaledX /= characterScaleX;
          } else if (width !== measuredWidth) {
            scaledX +=
              (((width - measuredWidth) / 2000) * fontSize) / fontSizeScale;
          }
        }
        
        
        if (this.contentVisible && (glyph.isInFont || font.missingFile)) {
          if (simpleFillText && !accent) {
            
            ctx.fillText(character, scaledX, scaledY);
          } else {
            this.paintChar(
              character,
              scaledX,
              scaledY,
              patternTransform,
              resetLineWidthToOne
            );
            if (accent) {
              const scaledAccentX =
                scaledX + (fontSize * accent.offset.x) / fontSizeScale;
              const scaledAccentY =
                scaledY - (fontSize * accent.offset.y) / fontSizeScale;