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)

const c = colorStops[i];
          grad.addColorStop(c[0], c[1]);
        }
        return grad;
      },
    };
  },
};
const createMeshCanvas = (function createMeshCanvasClosure() {
  function drawTriangle(data, context, p1, p2, p3, c1, c2, c3) {
    
    const coords = context.coords,
      colors = context.colors;
    const bytes = data.data,
      rowSize = data.width * 4;
    let tmp;
    if (coords[p1 + 1] > coords[p2 + 1]) {
      tmp = p1;
      p1 = p2;
      p2 = tmp;
      tmp = c1;
      c1 = c2;
      c2 = tmp;
    }
    if (coords[p2 + 1] > coords[p3 + 1]) {
      tmp = p2;
      p2 = p3;
      p3 = tmp;
      tmp = c2;
      c2 = c3;