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
let shouldScaleText = false;
  if (
    geom.str.length > 1 ||
    (task._enhanceTextSelection && AllWhitespaceRegexp.test(geom.str))
  ) {
    shouldScaleText = true;
  } else if (geom.transform[0] !== geom.transform[3]) {
    const absScaleX = Math.abs(geom.transform[0]),
      absScaleY = Math.abs(geom.transform[3]);
    
    
    if (
      absScaleX !== absScaleY &&
      Math.max(absScaleX, absScaleY) / Math.min(absScaleX, absScaleY) > 1.5
    ) {
      shouldScaleText = true;
    }
  }
  if (shouldScaleText) {
    if (style.vertical) {
      textDivProperties.canvasWidth = geom.height * task._viewport.scale;
    } else {
      textDivProperties.canvasWidth = geom.width * task._viewport.scale;
    }
  }
  task._textDivProperties.set(textDiv, textDivProperties);
  if (task._textContentStream) {
    task._layoutText(textDiv);