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.
ctx.restore();
        } else {
          
          ctx.lineWidth = Math.max(lineWidth, this.current.lineWidth);
          ctx.stroke();
        }
      }
    }
    if (consumePath) {
      this.consumePath(this.current.getClippedPathBoundingBox());
    }
    
    ctx.globalAlpha = this.current.fillAlpha;
  }
  closeStroke() {
    this.closePath();
    this.stroke();
  }
  fill(consumePath) {
    consumePath = typeof consumePath !== "undefined" ? consumePath : true;
    const ctx = this.ctx;
    const fillColor = this.current.fillColor;
    const isPatternFill = this.current.patternFill;
    let needRestore = false;
    if (isPatternFill) {
      ctx.save();
      ctx.fillStyle = fillColor.getPattern(
        ctx,
        this,
        ctx.mozCurrentTransformInverse,