Word file used: 
[Formular_T.docx](https://github.com/mozilla/pdf.js/files/6907859/Formular_T.docx)

PDFs generated:
PDF 1: [Formular_T_default.pdf](https://github.com/mozilla/pdf.js/files/6907771/Formular_T_default.pdf)
PDF 2: [Formular_T_changed.pdf](https://github.com/mozilla/pdf.js/files/6907772/Formular_T_changed.pdf)

- PDF.js version: v2.9.359

Steps to reproduce the problem:
1. Create Word Document with Checkbox and check it.
2. Convert Word document to PDF using **Aspose.pdf** (for .net)

3. Extra: Change value of second Checkbox  in PDF 1 and save the file (PDF 2). The new File will show both Checkboxes checked in other browser, but only the newly checked one in PDF.js

Expected:
Checkbox is checked (pdf viewer from adobe/Chrome Version 92.0.4515.107 64-bit)
![image](https://user-images.githubusercontent.com/76941221/127659557-42be1cca-3c90-49b8-b224-70ee85aa1b30.png)

Result:
Checkbox is not checked (Mozilla Firefox/PDF.js)
![image](https://user-images.githubusercontent.com/76941221/127660064-e3cdc3f9-6887-4ae7-af27-d46cded69029.png)



line = font.encodeString(line).join("");
    const glyphs = font.charsToGlyphs(line);
    if (glyphs.length <= 1) {
      
      return [line];
    }
    const positions = font.getCharPositions(line);
    const scale = fontSize / 1000;
    const chunks = [];
    let lastSpacePosInStringStart = -1,
      lastSpacePosInStringEnd = -1,
      lastSpacePos = -1,
      startChunk = 0,
      currentWidth = 0;
    for (let i = 0, ii = glyphs.length; i < ii; i++) {
      const [start, end] = positions[i];
      const glyph = glyphs[i];
      const glyphWidth = glyph.width * scale;
      if (glyph.unicode === " ") {
        if (currentWidth + glyphWidth > width) {
          
          chunks.push(line.substring(startChunk, start));
          startChunk = start;
          currentWidth = glyphWidth;
          lastSpacePosInStringStart = -1;
          lastSpacePos = -1;
        } else {
          currentWidth += glyphWidth;