fix panic when slice str

[zxlzy]

fix that #176

[imsnif]

Hey @zxlzy - following my comment here (#176 (comment)) would you like to adjust the function like in diskonaut: https://github.com/imsnif/diskonaut/blob/main/src/ui/format/truncate.rs#L17-L37 ?
If I'm not mistaken, I think this is mostly copy/pasting and making sure tests/formatting pass (and that it solves the problem for you). Would be happy to hear your thoughts.

[zxlzy]

@imsnif You are right. I have copy some code from diskonaut and make sure it passed all existing test cases. Because of I am a greenhand of rust programming. I can't add test cases for split Chinese for now.

[imsnif]

Hey @zxlzy, thanks for this! I don't think it's critical to add test cases for this. It looks good to me. I'll fix the CI issues on main.