Current master d5622eb6ff, font display issue.

[Zhu Zihao]

I'm using Sarasa Gothic Mono font, which force a CJK character has equivalent
width with 2 latin character. But in commit d5622eb6ff, A table seems to have
misalignment issue.

For example, check this table generated by org in Emacs.

| English | 中文 |   |   |   |
|---------+------+---+---+---|
|         |      |   |   |   |

And I attach two picture, the black backgroud is in Emacs, white one is in
Firefox.

<#part type="image/png" filename="/home/chino/tmp/in-emacs.png" 
disposition=attachment description="The display in Emacs">
<#/part>
<#part type="image/png" filename="/home/chino/tmp/in-firefox.png" 
disposition=attachment description="Display in Firefox">
<#/part>

And here is the homepage of Sarasa Gothic: 
https://github.com/be5invis/Sarasa-Gothic/