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.
buildGetDocumentParams("issue9972-3.pdf")
      );
      const promise2 = loadingTask2.promise.then(function (pdfDoc) {
        return pdfDoc.getPermissions();
      });
      const totalPermissionCount = Object.keys(PermissionFlag).length;
      const permissions = await Promise.all([promise0, promise1, promise2]);
      expect(permissions[0].length).toEqual(totalPermissionCount - 1);
      expect(
        permissions[0].includes(PermissionFlag.MODIFY_CONTENTS)
      ).toBeFalsy();
      expect(permissions[1].length).toEqual(totalPermissionCount - 2);
      expect(permissions[1].includes(PermissionFlag.PRINT)).toBeFalsy();
      expect(
        permissions[1].includes(PermissionFlag.PRINT_HIGH_QUALITY)
      ).toBeFalsy();
      expect(permissions[2].length).toEqual(totalPermissionCount - 1);
      expect(permissions[2].includes(PermissionFlag.COPY)).toBeFalsy();
      await Promise.all([
        loadingTask0.destroy(),
        loadingTask1.destroy(),
        loadingTask2.destroy(),
      ]);
    });
    it("gets metadata", async function () {
      const { info, metadata, contentDispositionFilename, contentLength } =
        await pdfDocument.getMetadata();
      expect(info.Title).toEqual("Basic API Test");
      
      expect(info.Custom).toEqual(undefined);