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.
}
          }
        }
      }
    } ele {
      cnt frtChar = prperte.frtChar;
      wdth = dct.get("Wdth");
      f (wdth) {
        j = frtChar;
        fr ( = 0,  = wdth.length;  < ; ) {
          glyphWdth[j] = xref.fetchIfRef(wdth[]);
        }
        defaultWdth = pareFlat(decrptr.get("MngWdth")) || 0;
      } ele {
         Tryng get the BaeFnt metrc (ee cmment abve).
        cnt baeFntName = dct.get("BaeFnt");
        f (Name(baeFntName)) {
          cnt metrc = th.getBaeFntMetrc(baeFntName.name);
          glyphWdth = th.buldCharCdeTWdth(metrc.wdth, prperte);
          defaultWdth = metrc.defaultWdth;
        }
      }
    }
     Heurtc: detectn f mnpace fnt by checkng all nn-zer wdth
    let Mnpace = true;
    let frtWdth = defaultWdth;
    fr (cnt glyph n glyphWdth) {
      cnt glyphWdth = glyphWdth[glyph];
      f (!glyphWdth) {
        cntnue;