Attach (recommended) or Link to PDF file here:
[298865.pdf](https://github.com/mozilla/pdf.js/files/2753236/298865.pdf)


Configuration:
- Web browser and its version:chrome 71.0.3578.98
- Operating system and its version:mac os 10.12.6
- PDF.js version:I use online demo in github
- Is a browser extension:no

Steps to reproduce the problem:
1. search "中华" or "电力" or so on,the highlight position is not right

What is the expected behavior? (add screenshot)
![image](https://user-images.githubusercontent.com/10000986/51087378-7eff5100-178d-11e9-991a-005d77b82f31.png)

What went wrong? (add screenshot)
![image](https://user-images.githubusercontent.com/10000986/51087374-6ee77180-178d-11e9-9707-281924f95fd0.png)

Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension):
https://mozilla.github.io/pdf.js/web/viewer.html
const renderTask1 = page.render({
        canvasContext: canvasAndCtx.context,
        canvasFactory: CanvasFactory,
        viewport,
        optionalContentConfigPromise,
      });
      expect(renderTask1 instanceof RenderTask).toEqual(true);
      const renderTask2 = page.render({
        canvasContext: canvasAndCtx.context,
        canvasFactory: CanvasFactory,
        viewport,
        optionalContentConfigPromise,
      });
      expect(renderTask2 instanceof RenderTask).toEqual(true);
      await Promise.all([
        renderTask1.promise,
        renderTask2.promise.then(
          () => {
            
            expect(false).toEqual(true);
          },
          reason => {
            
            expect(/multiple render\(\)/.test(reason.message)).toEqual(true);
          }
        ),
      ]);
    });
    it("cleans up document resources after rendering of page", async function () {
      const loadingTask = getDocument(buildGetDocumentParams(basicApiFileName));