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 currentImgData = objsPool.get(objId);
          expect(currentImgData.width).toEqual(firstImgData.width);
          expect(currentImgData.height).toEqual(firstImgData.height);
          expect(currentImgData.kind).toEqual(firstImgData.kind);
          expect(currentImgData.data instanceof Uint8ClampedArray).toEqual(
            true
          );
          expect(
            currentImgData.data.every((value, index) => {
              return value === firstImgData.data[index];
            })
          ).toEqual(true);
        }
      }
      await loadingTask.destroy();
      firstImgData = null;
    });
  });
  describe("Multiple `getDocument` instances", function () {
    
    
    const pdf1 = buildGetDocumentParams("tracemonkey.pdf");
    
    const pdf2 = buildGetDocumentParams("TAMReview.pdf");
    
    const pdf3 = buildGetDocumentParams("issue6068.pdf");
    const loadingTasks = [];
    
    
    async function renderPDF(filename) {