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)

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);