Make FilePath::GetCurrentDir() not returning trailing slash on Windows

[sergio-nsk]

trafficstars

It returned the trailing backslash if the current working directory was a root directory. It should be consistent w/ all cases.

_getcwd, _wgetcwd

_getcwd returns a string that represents the path of the current working directory. If the current working directory is the root, the string ends with a backslash (\). If the current working directory is a directory other than the root, the string ends with the directory name and not with a backslash.