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 coords = mesh.coords;
    const colors = mesh.colors;
    const ps = []; 
    while (reader.hasData) {
      const coord = reader.readCoordinate();
      const color = reader.readComponents();
      ps.push(coords.length);
      coords.push(coord);
      colors.push(color);
    }
    mesh.figures.push({
      type: "lattice",
      coords: new Int32Array(ps),
      colors: new Int32Array(ps),
      verticesPerRow,
    });
  }
  const MIN_SPLIT_PATCH_CHUNKS_AMOUNT = 3;
  const MAX_SPLIT_PATCH_CHUNKS_AMOUNT = 20;
  const TRIANGLE_DENSITY = 20; 
  const getB = (function getBClosure() {
    function buildB(count) {