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)

let k;
      if (y < y1) {
        k = 0;
      } else if (y > y3) {
        k = 1;
      } else {
        k = (y1 - y) / (y1 - y3);
      }
      xb = x1 - (x1 - x3) * k;
      cbr = c1r - (c1r - c3r) * k;
      cbg = c1g - (c1g - c3g) * k;
      cbb = c1b - (c1b - c3b) * k;
      const x1_ = Math.round(Math.min(xa, xb));
      const x2_ = Math.round(Math.max(xa, xb));
      let j = rowSize * y + x1_ * 4;
      for (let x = x1_; x <= x2_; x++) {
        k = (xa - x) / (xa - xb);
        if (k < 0) {
          k = 0;
        } else if (k > 1) {
          k = 1;
        }
        bytes[j++] = (car - (car - cbr) * k) | 0;
        bytes[j++] = (cag - (cag - cbg) * k) | 0;
        bytes[j++] = (cab - (cab - cbb) * k) | 0;
        bytes[j++] = 255;
      }
    }
  }
  function drawFigure(data, figure, context) {