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.
changedHorizon[0].start = boundary.y1;
      changedHorizon.unshift({
        start: horizon[i].start,
        end: boundary.y1,
        boundary: horizon[i].boundary,
      });
    }
    if (boundary.y2 < horizon[j].end) {
      changedHorizon[changedHorizon.length - 1].end = boundary.y2;
      changedHorizon.push({
        start: boundary.y2,
        end: horizon[j].end,
        boundary: horizon[j].boundary,
      });
    }
    
    
    
    for (q = i; q <= j; q++) {
      horizonPart = horizon[q];
      affectedBoundary = horizonPart.boundary;
      if (affectedBoundary.x2New !== undefined) {
        continue;
      }
      let used = false;
      for (
        k = i - 1;
        !used && k >= 0 && horizon[k].start >= affectedBoundary.y1;
        k--
      ) {