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.
}
  setCharWidthAndBounds(xWidth, yWidth, llx, lly, urx, ury) {
    
    
    this.ctx.rect(llx, lly, urx - llx, ury - lly);
    this.clip();
    this.endPath();
  }
  
  getColorN_Pattern(IR) {