This is a regression from #12864. The underscore is now too thin when the document is zoomed in.

URL: https://github.com/mozilla/pdf.js/files/2321540/issue6127.pdf
PDF.js 2.7.526: https://i.imgur.com/T4mIpct.png
PDF.js 2.7.510: https://i.imgur.com/nbwEpGT.png
Adobe Acrobat Reader DC 2020.013.20074: https://i.imgur.com/wDFBf3R.png

The screenshots were taken at 400% zoom.
case OPS.curveTo3:
          startX = x;
          startY = y;
          x = args[j + 2];
          y = args[j + 3];
          ctx.bezierCurveTo(args[j], args[j + 1], x, y, x, y);
          current.updateCurvePathMinMax(
            ctx.mozCurrentTransform,
            startX,
            startY,
            args[j],
            args[j + 1],
            x,
            y,
            x,
            y
          );
          j += 4;
          break;
        case OPS.closePath:
          ctx.closePath();
          break;
      }
    }
    current.setCurrentPoint(x, y);
  }
  closePath() {
    this.ctx.closePath();
  }
  stroke(consumePath) {