Issue with checkbox checking and unicode

[gregzawadzki]

• Gitea version (or commit ref):
• Git version:. 15.0+dev-411-g2b3935744
  It's reproducable on try.gitea.io aswell as on my docker 1.14.2

If I create issue with checkboxes

- [ ] Mrówka testowa
- [ ] Źródło piąte
- [ ] Część 1
- [ ] Część trzecia 1

It's created OK but when I check all checkboxes and hit f5 to refresh page:

Code becomes

- [x] Mrówka testowa
- [ x Źródło piąte
- [ ] Czxść 1
- [ ] Częśćxtrzecia 1

It seems that while "Checking" checkbox it assumes all characters are only 8 bits and ignores 16 bits ones (probably higher ones too)