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)

cl[0] = ((c0[0] * (splitYBy - row) + c2[0] * row) / splitYBy) | 0;
      cl[1] = ((c0[1] * (splitYBy - row) + c2[1] * row) / splitYBy) | 0;
      cl[2] = ((c0[2] * (splitYBy - row) + c2[2] * row) / splitYBy) | 0;
      cr[0] = ((c1[0] * (splitYBy - row) + c3[0] * row) / splitYBy) | 0;
      cr[1] = ((c1[1] * (splitYBy - row) + c3[1] * row) / splitYBy) | 0;
      cr[2] = ((c1[2] * (splitYBy - row) + c3[2] * row) / splitYBy) | 0;
      for (let col = 0; col <= splitXBy; col++, k++) {
        if (
          (row === 0 || row === splitYBy) &&
          (col === 0 || col === splitXBy)
        ) {
          continue;
        }
        let x = 0,
          y = 0;
        let q = 0;
        for (let i = 0; i <= 3; i++) {
          for (let j = 0; j <= 3; j++, q++) {
            const m = bRow[row][i] * bCol[col][j];
            x += coords[pi[q]][0] * m;
            y += coords[pi[q]][1] * m;
          }
        }
        figureCoords[k] = coords.length;
        coords.push([x, y]);
        figureColors[k] = colors.length;
        const newColor = new Uint8Array(3);
        newColor[0] = ((cl[0] * (splitXBy - col) + cr[0] * col) / splitXBy) | 0;
        newColor[1] = ((cl[1] * (splitXBy - col) + cr[1] * col) / splitXBy) | 0;
        newColor[2] = ((cl[2] * (splitXBy - col) + cr[2] * col) / splitXBy) | 0;