Attach (recommended) or Link to PDF file here:
https://bitcoin.org/bitcoin.pdf

Configuration:
- Web browser and its version: all
- Operating system and its version: all
- PDF.js version: tested with 2.9.11, but most likely all versions
- Is a browser extension: no

Steps to reproduce the problem:
1. Type "a purely" (single space between "a" and "purely") - doesn't find anything
2. Type "a  purely" (two spaces between "a" and "purely") - finds the phrase

Sometimes even 3 spaces are necessary.

What is the expected behavior? (add screenshot)
![Screenshot from 2021-04-08 13-00-03](https://user-images.githubusercontent.com/6362989/114008903-57639a00-986b-11eb-903a-92bbebbd922b.png)

What went wrong? (add screenshot)
![Screenshot from 2021-04-08 13-01-53](https://user-images.githubusercontent.com/6362989/114008810-44e96080-986b-11eb-8232-f58a62ed7899.png)

This affects many PDFs because justify alignment is common enough.
descent = 0;
  for (let i = pixels.length - 1 - 3; i >= 0; i -= 4) {
    if (pixels[i] > 0) {
      descent = Math.ceil(i / 4 / DEFAULT_FONT_SIZE);
      break;
    }
  }
  
  
  
  ctx.clearRect(0, 0, DEFAULT_FONT_SIZE, DEFAULT_FONT_SIZE);
  ctx.strokeText("A", 0, DEFAULT_FONT_SIZE);
  pixels = ctx.getImageData(0, 0, DEFAULT_FONT_SIZE, DEFAULT_FONT_SIZE).data;
  ascent = 0;
  for (let i = 0, ii = pixels.length; i < ii; i += 4) {
    if (pixels[i] > 0) {
      ascent = DEFAULT_FONT_SIZE - Math.floor(i / 4 / DEFAULT_FONT_SIZE);
      break;
    }
  }
  ctx.restore();
  if (ascent) {
    const ratio = ascent / (ascent + descent);
    ascentCache.set(fontFamily, ratio);
    return ratio;
  }
  ascentCache.set(fontFamily, DEFAULT_FONT_ASCENT);
  return DEFAULT_FONT_ASCENT;
}
function appendText(task, geom, styles, ctx) {