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 splitXBy = Math.ceil(
      ((figureMaxX - figureMinX) * TRIANGLE_DENSITY) /
        (mesh.bounds[2] - mesh.bounds[0])
    );
    splitXBy = Math.max(
      MIN_SPLIT_PATCH_CHUNKS_AMOUNT,
      Math.min(MAX_SPLIT_PATCH_CHUNKS_AMOUNT, splitXBy)
    );
    let splitYBy = Math.ceil(
      ((figureMaxY - figureMinY) * TRIANGLE_DENSITY) /
        (mesh.bounds[3] - mesh.bounds[1])
    );
    splitYBy = Math.max(
      MIN_SPLIT_PATCH_CHUNKS_AMOUNT,
      Math.min(MAX_SPLIT_PATCH_CHUNKS_AMOUNT, splitYBy)
    );
    const verticesPerRow = splitXBy + 1;
    const figureCoords = new Int32Array((splitYBy + 1) * verticesPerRow);
    const figureColors = new Int32Array((splitYBy + 1) * verticesPerRow);
    let k = 0;
    const cl = new Uint8Array(3),
      cr = new Uint8Array(3);
    const c0 = colors[ci[0]],
      c1 = colors[ci[1]],
      c2 = colors[ci[2]],
      c3 = colors[ci[3]];
    const bRow = getB(splitYBy),
      bCol = getB(splitXBy);
    for (let row = 0; row <= splitYBy; row++) {