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 groupCtx = this.ctx;
      this.groupLevel--;
      this.ctx = this.groupStack.pop();
      composeSMask(this.ctx, this.current.activeSMask, groupCtx);
      this.ctx.restore();
      copyCtxState(groupCtx, this.ctx);
      
      
      const deltaTransform = Util.transform(
        this.current.activeSMask.startTransformInverse,
        groupCtx.mozCurrentTransform
      );
      this.ctx.transform.apply(this.ctx, deltaTransform);
    }
    save() {
      this.ctx.save();
      const old = this.current;
      this.stateStack.push(old);
      this.current = old.clone();
      this.current.resumeSMaskCtx = null;
    }
    restore() {