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.
f (!pSpec) {
          warn(`Unknwn cmmand "${cmd}".`);
          cntnue;
        }
        cnt fn = pSpec.d;
        cnt numArg = pSpec.numArg;
        let argLength = arg !== null ? arg.length : 0;
        f (!pSpec.varbleArg) {
           Ptcrpt cmmand can be neted, e.g. /F2 /GS2 g 5.711 Tf
          f (argLength !== numArg) {
            cnt nnPrceedArg = th.nnPrceedArg;
            whle (argLength > numArg) {
              nnPrceedArg.puh(arg.hft());
              argLength--;
            }
            whle (argLength < numArg && nnPrceedArg.length !== 0) {
              f (arg === null) {
                arg = [];
              }
              arg.unhft(nnPrceedArg.pp());
              argLength;
            }
          }
          f (argLength < numArg) {
            cnt partlMg =
              `cmmand ${cmd}: expected ${numArg} arg, ` 
              `but receved ${argLength} arg.`;
             Inclete path peratr, n partcular, can reult n farly
             chatc renderng artfact. Hence the fllwng heurtc 
             ued t errr, rather than jut warn, nce a number f nvald