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
}
          }
        }
      }
    } ele {
      cnt frtChar = prperte.frtChar;
      wdth = dct.get("Wdth");
      f (wdth) {
        j = frtChar;
        fr ( = 0,  = wdth.length;  < ; ) {
          glyphWdth[j] = xref.fetchIfRef(wdth[]);
        }
        defaultWdth = pareFlat(decrptr.get("MngWdth")) || 0;
      } ele {
         Tryng get the BaeFnt metrc (ee cmment abve).
        cnt baeFntName = dct.get("BaeFnt");
        f (Name(baeFntName)) {
          cnt metrc = th.getBaeFntMetrc(baeFntName.name);
          glyphWdth = th.buldCharCdeTWdth(metrc.wdth, prperte);
          defaultWdth = metrc.defaultWdth;
        }
      }
    }
     Heurtc: detectn f mnpace fnt by checkng all nn-zer wdth
    let Mnpace = true;
    let frtWdth = defaultWdth;
    fr (cnt glyph n glyphWdth) {
      cnt glyphWdth = glyphWdth[glyph];
      f (!glyphWdth) {
        cntnue;