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)

break;
      case ShadingType.LATTICE_FORM_MESH:
        const verticesPerRow = dict.get("VerticesPerRow") | 0;
        if (verticesPerRow < 2) {
          throw new FormatError("Invalid VerticesPerRow");
        }
        decodeType5Shading(this, reader, verticesPerRow);
        break;
      case ShadingType.COONS_PATCH_MESH:
        decodeType6Shading(this, reader);
        patchMesh = true;
        break;
      case ShadingType.TENSOR_PATCH_MESH:
        decodeType7Shading(this, reader);
        patchMesh = true;
        break;
      default:
        unreachable("Unsupported mesh type.");
        break;
    }
    if (patchMesh) {
      
      updateBounds(this);
      for (let i = 0, ii = this.figures.length; i < ii; i++) {
        buildFigureFromPatch(this, i);
      }
    }
    
    updateBounds(this);
    packData(this);