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
used = horizon[k].boundary === affectedBoundary;
      }
      for (
        k = j + 1;
        !used && k < horizon.length && horizon[k].end <= affectedBoundary.y2;
        k++
      ) {
        used = horizon[k].boundary === affectedBoundary;
      }
      for (k = 0; !used && k < changedHorizon.length; k++) {
        used = changedHorizon[k].boundary === affectedBoundary;
      }
      if (!used) {
        affectedBoundary.x2New = maxXNew;
      }
    }
    Array.prototype.splice.apply(
      horizon,
      [i, j - i + 1].concat(changedHorizon)
    );
  }
  
  for (const horizonPart of horizon) {
    const affectedBoundary = horizonPart.boundary;
    if (affectedBoundary.x2New === undefined) {
      affectedBoundary.x2New = Math.max(width, affectedBoundary.x2);
    }
  }
}
class TextLayerRenderTask {