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.
const intersect = Util.intersect(this.clipBox, this.getPathBoundingBox());
    this.startNewPathAndClipBox(intersect || [0, 0, 0, 0]);
  }
  startNewPathAndClipBox(box) {
    this.clipBox = box;
    this.minX = Infinity;
    this.minY = Infinity;
    this.maxX = 0;
    this.maxY = 0;
  }
  getClippedPathBoundingBox(pathType = PathType.FILL, transform = null) {
    return Util.intersect(
      this.clipBox,
      this.getPathBoundingBox(pathType, transform)
    );
  }
}
function putBinaryImageData(ctx, imgData, transferMaps = null) {