Libgit2 partially forwards OS error message texts.
On non-english Windows OSes these errors may contain non-ascii characters (i.e. umlauts).
To avoid that a UnicodeDecodeError is raised the error message is interpreted as UTF-8.
The solution should not be necessary on linux/osx as they return always ascii (as far as I know).
Thus this solution will not change the behaviour on linux/osx.