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 viewport = page.getViewport({ scale: 1 });
      const canvasAndCtx = CanvasFactory.create(
        viewport.width,
        viewport.height
      );
      const renderTask = page.render({
        canvasContext: canvasAndCtx.context,
        canvasFactory: CanvasFactory,
        viewport,
      });
      expect(renderTask instanceof RenderTask).toEqual(true);
      renderTask.cancel();
      try {
        await renderTask.promise;
        
        expect(false).toEqual(true);
      } catch (reason) {
        expect(reason instanceof RenderingCancelledException).toEqual(true);
        expect(reason.message).toEqual("Rendering cancelled, page 1");
        expect(reason.type).toEqual("canvas");
      }
      CanvasFactory.destroy(canvasAndCtx);
    });
    it("re-render page, using the same canvas, after cancelling rendering", async function () {
      const viewport = page.getViewport({ scale: 1 });
      const canvasAndCtx = CanvasFactory.create(
        viewport.width,
        viewport.height
      );
      const renderTask = page.render({