Attach (recommended) or Link to PDF file here:

Configuration:
- Web browser and its version: Chrome 90.0.4430.93
- Operating system and its version: macOs Big Sur 11.2.3
- PDF.js version: 2.7.570
- Is a browser extension: No

Steps to reproduce the problem:
1. Load the attached pdf in https://mozilla.github.io/pdf.js/web/viewer.html
2. Go to page 46. Dotted lines are missing in the graphics (see screenshot from acrobat reader)

What is the expected behavior? (add screenshot) See the screenshot
[Technical_Guide_UK.pdf](https://github.com/mozilla/pdf.js/files/6413001/Technical_Guide_UK.pdf)
![Screenshot 2021-05-03 at 07 46 09](https://user-images.githubusercontent.com/3785784/116844541-a343fd80-abe3-11eb-94c3-d03b3dfd6769.png)

ctx.save();
        ctx.transform(
          scaleX,
          skewX,
          skewY,
          scaleY,
          positions[i],
          positions[i + 1]
        );
        ctx.scale(1, -1);
        ctx.drawImage(maskCanvas.canvas, 0, 0, width, height, 0, -1, 1, 1);
        ctx.restore();
      }
    }
    paintImageMaskXObjectGroup(images) {
      if (!this.contentVisible) {
        return;
      }
      const ctx = this.ctx;
      const fillColor = this.current.fillColor;
      const isPatternFill = this.current.patternFill;
      for (let i = 0, ii = images.length; i < ii; i++) {
        const image = images[i];
        const width = image.width,
          height = image.height;
        const maskCanvas = this.cachedCanvases.getCanvas(
          "maskCanvas",
          width,
          height
        );