unable to subset certain characters
My steps for reproduction
1. get http://www.apple.com/wss/fonts/PingHei/v1/PingHei-light.woff
2. convert into ttf via https://andrewsun.com/projects/woffjs/woffer-woff-font-converter/
3. use [character-map](https://github.com/bitinn/character-map) to produce the glyph map string like `character-map -f pinghei.ttf > map.txt`
4. try to subset the same ttf file, `fontmin -t `cat map.txt` pinghei.ttf > subset.ttf`
5. `character-map -f subset.ttf > map2.txt`

Compare `map.txt` and `map2.txt`, some obscure glyph appear to be missing (most chinese fonts appear to be intact though).

If we only do `fontmin pinghei.ttf > subset.ttf` the character map doesn't change, so I am guessing some characters are not allowed by your `-t` settings.
