search addon doesn't work well with chinese

[zjjEcho]

I found some related issues, like this emoji issue
But it doesn't seem to solve my problem.

Details

• Browser and browser version: chrome(52.0.2743.82 64-bit)
• OS version: Ubuntu 16.04 LTS
• xterm.js version: 3.8.0

Steps to reproduce

1. generate test content with some chinese in it
2. search some content，like this
   

if there's no chinese before the search content, search addon works fine, like this

[jerch]

This is prolly related to #1686.