Attach (recommended) or Link to PDF file here:
[Hong Kong Aircraft Engineering Company Limited_1511417616.1 2.pdf](https://github.com/mozilla/pdf.js/files/1539395/Hong.Kong.Aircraft.Engineering.Company.Limited_1511417616.1.2.pdf)


Configuration:
- Web browser and its version: Chrome: 63 
- Operating system and its version: windows and macOs
- PDF.js version: 2.0.185
- Is a browser extension: No

Steps to reproduce the problem:
1. Upload the above PDF and search for "article 1"
2. PDF.js showing only **2** match But actually **4** times available.   

What is the expected behavior? (add screenshot)

![screen shot 2017-12-07 at 7](https://user-images.githubusercontent.com/6101789/33720106-ed404576-db88-11e7-9c19-cf6aea74e9f3.png)



What went wrong? (add screenshot)

Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension):

const cachedAscent = ascentCache.get(fontFamily);
  if (cachedAscent) {
    return cachedAscent;
  }
  ctx.save();
  ctx.font = `${DEFAULT_FONT_SIZE}px ${fontFamily}`;
  const metrics = ctx.measureText("");
  
  let ascent = metrics.fontBoundingBoxAscent;
  let descent = Math.abs(metrics.fontBoundingBoxDescent);
  if (ascent) {
    ctx.restore();
    const ratio = ascent / (ascent + descent);
    ascentCache.set(fontFamily, ratio);
    return ratio;
  }
  
  
  
  
  ctx.strokeStyle = "red";
  ctx.clearRect(0, 0, DEFAULT_FONT_SIZE, DEFAULT_FONT_SIZE);
  ctx.strokeText("g", 0, 0);
  let pixels = ctx.getImageData(
    0,
    0,
    DEFAULT_FONT_SIZE,
    DEFAULT_FONT_SIZE
  ).data;