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.
it("gets fingerprints", function () {
      expect(pdfDocument.fingerprints).toEqual([
        "ea8b35919d6279a369e835bde778611b",
        null,
      ]);
    });
    it("gets fingerprints, from modified document", async function () {
      const loadingTask = getDocument(
        buildGetDocumentParams("annotation-tx.pdf")
      );
      const pdfDoc = await loadingTask.promise;
      expect(pdfDoc.fingerprints).toEqual([
        "3ebd77c320274649a68f10dbf3b9f882",
        "e7087346aa4b4ae0911c1f1643b57345",
      ]);
      await loadingTask.destroy();
    });
    it("gets page", async function () {
      const data = await pdfDocument.getPage(1);
      expect(data instanceof PDFPageProxy).toEqual(true);
      expect(data.pageNumber).toEqual(1);
    });
    it("gets non-existent page", async function () {
      let outOfRangePromise = pdfDocument.getPage(100);
      let nonIntegerPromise = pdfDocument.getPage(2.5);
      let nonNumberPromise = pdfDocument.getPage("1");
      outOfRangePromise = outOfRangePromise.then(
        function () {
          throw new Error("shall fail for out-of-range pageNumber parameter");
        },