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.
const renderTask = pdfPage.render({
        canvasContext: canvasAndCtx.context,
        canvasFactory: CanvasFactory,
        viewport,
      });
      expect(renderTask instanceof RenderTask).toEqual(true);
      
      renderTask.onContinue = function (cont) {
        waitSome(cont);
      };
      try {
        await pdfDoc.cleanup();
        
        expect(false).toEqual(true);
      } catch (reason) {
        expect(reason instanceof Error).toEqual(true);
        expect(reason.message).toEqual(
          "startCleanup: Page 1 is currently rendering."
        );
      }
      await renderTask.promise;
      CanvasFactory.destroy(canvasAndCtx);
      await loadingTask.destroy();
    });
    it("caches image resources at the document/page level as expected (issue 11878)", async function () {
      const { NUM_PAGES_THRESHOLD } = GlobalImageCache,
        EXPECTED_WIDTH = 2550,
        EXPECTED_HEIGHT = 3300;
      const loadingTask = getDocument(buildGetDocumentParams("issue11878.pdf"));
      const pdfDoc = await loadingTask.promise;