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 glyph = glyphs[i];
        if (isNum(glyph)) {
          x += (spacingDir * glyph * fontSize) / 1000;
          continue;
        }
        let restoreNeeded = false;
        const spacing = (glyph.isSpace ? wordSpacing : 0) + charSpacing;
        const character = glyph.fontChar;
        const accent = glyph.accent;
        let scaledX, scaledY;
        let width = glyph.width;
        if (vertical) {
          const vmetric = glyph.vmetric || defaultVMetrics;
          const vx =
            -(glyph.vmetric ? vmetric[1] : width * 0.5) * widthAdvanceScale;
          const vy = vmetric[2] * widthAdvanceScale;
          width = vmetric ? -vmetric[0] : width;
          scaledX = vx / fontSizeScale;
          scaledY = (x + vy) / fontSizeScale;
        } else {
          scaledX = x / fontSizeScale;
          scaledY = 0;
        }
        if (font.remeasure && width > 0) {
          
          
          
          const measuredWidth =
            ((ctx.measureText(character).width * 1000) / fontSize) *
            fontSizeScale;