Attach (recommended) or Link to PDF file here:
[example.pdf](https://github.com/mozilla/pdf.js/files/6916129/example.pdf)

Configuration:
- Web browser and its version: Chrome, Firefox
- Operating system and its version: all
- PDF.js version: various versions, including 2.11.54
- Is a browser extension: no

Screenshot with visible textLayer:
![Screenshot from 2021-08-02 13-05-03](https://user-images.githubusercontent.com/6362989/127844878-f85e291f-2060-4028-be09-7835f32ccfaa.png)

Which means some letters at the beginning/end of text selection are missing when copying text.

this.capHeight = properties.capHeight / PDF_GLYPH_SPACE_UNITS;
    this.ascent = properties.ascent / PDF_GLYPH_SPACE_UNITS;
    this.descent = properties.descent / PDF_GLYPH_SPACE_UNITS;
    this.lineHeight = this.ascent - this.descent;
    this.fontMatrix = properties.fontMatrix;
    this.bbox = properties.bbox;
    this.defaultEncoding = properties.defaultEncoding;
    this.toUnicode = properties.toUnicode;
    this.toFontChar = [];
    if (properties.type === "Type3") {
      for (let charCode = 0; charCode < 256; charCode++) {
        this.toFontChar[charCode] =
          this.differences[charCode] || properties.defaultEncoding[charCode];
      }
      this.fontType = FontType.TYPE3;
      return;
    }
    this.cidEncoding = properties.cidEncoding;
    this.vertical = !!properties.vertical;
    if (this.vertical) {
      this.vmetrics = properties.vmetrics;
      this.defaultVMetrics = properties.defaultVMetrics;
    }
    if (!file || file.isEmpty) {
      if (file) {
        
        
        warn('Font file is empty in "' + name + '" (' + this.loadedName + ")");
      }
      this.fallbackToSystemFont(properties);