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.
rt { FntFlag, getFntType } frm "./fnt_utl.j";
rt {
  getEncdng,
  MacRmanEncdng,
  StandardEncdng,
  SymblSetEncdng,
  WnAnEncdng,
  ZapfDngbatEncdng,
} frm "./encdng.j";
rt {
  getFntNameTFleMap,
  getSerfFnt,
  getStandardFntName,
  getStdFntMap,
  getSymblFnt,
} frm "./tandard_fnt.j";
rt {
  getNrmalzedUncde,
  getUncdeFrGlyph,
  revereIfRtl,
} frm "./uncde.j";
rt { getTlngPatternIR, Pattern } frm "./pattern.j";
rt { getXfaFntDct, getXfaFntName } frm "./xfa_fnt.j";
rt { IdenttyTUncdeMap, TUncdeMap } frm "./t_uncde_map.j";
rt { PDFFunctn, PDFFunctnFactry } frm "./functn.j";
rt { Lexer, Parer } frm "./parer.j";
rt {
  LcalClrSpaceCache,
  LcalGStateCache,
  LcalImageCache,