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 scale =
        bitsPerComponent < 32
          ? 1 / ((1 << bitsPerComponent) - 1)
          : 2.3283064365386963e-10; 
      const decode = this.context.decode;
      const components = this.tmpCompsBuf;
      for (let i = 0, j = 4; i < numComps; i++, j += 2) {
        const ci = this.readBits(bitsPerComponent);
        components[i] = ci * scale * (decode[j + 1] - decode[j]) + decode[j];
      }
      const color = this.tmpCsCompsBuf;
      if (this.context.colorFn) {
        this.context.colorFn(components, 0, color, 0);
      }
      return this.context.colorSpace.getRgb(color, 0);
    },
  };
  function decodeType4Shading(mesh, reader) {
    const coords = mesh.coords;
    const colors = mesh.colors;
    const operators = [];
    const ps = []; 
    let verticesLeft = 0; 
    while (reader.hasData) {
      const f = reader.readFlag();
      const coord = reader.readCoordinate();
      const color = reader.readComponents();
      if (verticesLeft === 0) {
        
        if (!(0 <= f && f <= 2)) {