access: file: simplify the check of remote path on Windows
PathIsNetworkPathW() is a basic function that only checks for \\
and
[a-zA-Z]:\\
pathes [1]. It's also not available on UWP apps.
We can do the same by checking the UTF-8 string directly without even a conversion to wide char string.
[1] https://docs.microsoft.com/en-us/windows/win32/api/shlwapi/nf-shlwapi-pathisnetworkpathw
Edited by Steve Lhomme