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.
expect(opListAnnotEnable.lastChunk).toEqual(true);
      const opListAnnotEnableForms = await pdfPage.getOperatorList({
        annotationMode: AnnotationMode.ENABLE_FORMS,
      });
      expect(opListAnnotEnableForms.fnArray.length).toBeGreaterThan(40);
      expect(opListAnnotEnableForms.argsArray.length).toBeGreaterThan(40);
      expect(opListAnnotEnableForms.lastChunk).toEqual(true);
      const opListAnnotEnableStorage = await pdfPage.getOperatorList({
        annotationMode: AnnotationMode.ENABLE_STORAGE,
      });
      expect(opListAnnotEnableStorage.fnArray.length).toBeGreaterThan(170);
      expect(opListAnnotEnableStorage.argsArray.length).toBeGreaterThan(170);
      expect(opListAnnotEnableStorage.lastChunk).toEqual(true);
      
      expect(opListAnnotDisable.fnArray.length).toBeLessThan(
        opListAnnotEnableForms.fnArray.length
      );
      expect(opListAnnotEnableForms.fnArray.length).toBeLessThan(
        opListAnnotEnable.fnArray.length
      );
      expect(opListAnnotEnable.fnArray.length).toBeLessThan(
        opListAnnotEnableStorage.fnArray.length
      );
      await loadingTask.destroy();
    });
    it("gets document stats after parsing page", async function () {
      const stats = await page.getOperatorList().then(function () {
        return pdfDocument.getStats();
      });
      const expectedStreamTypes = {};