Git: Fix config encoding on Windows

This fixes commit d72b4851b45ace311f8813fd4854a2a8e36ab8af
which has removed the conversion from Utf-8 on Windows.

Task-number: QTCREATORBUG-12092
Change-Id: I83c4d2d5eacb79ca99ef0b6f385344689582079e
Reviewed-by: Orgad Shaneh <orgads@gmail.com>