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.
current.updatePathMinMax(ctx.mozCurrentTransform, x, y);
          break;
        case OPS.lineTo:
          x = args[j++];
          y = args[j++];
          ctx.lineTo(x, y);
          current.updatePathMinMax(ctx.mozCurrentTransform, x, y);
          break;
        case OPS.curveTo:
          startX = x;
          startY = y;
          x = args[j + 4];
          y = args[j + 5];
          ctx.bezierCurveTo(
            args[j],
            args[j + 1],
            args[j + 2],
            args[j + 3],
            x,
            y
          );
          current.updateCurvePathMinMax(
            ctx.mozCurrentTransform,
            startX,
            startY,
            args[j],
            args[j + 1],
            args[j + 2],
            args[j + 3],
            x,