Windows code is probably still not quite right

[evilpie]

If the path length changes (file move?) between the GetFinalPathNameByHandleW calls we are going to be in trouble. I feel like I should just copy the fill_utf16_buf code in rust.

[evilpie]

I think 22bdbbf should be enough to at least make this method safe by adding the len2 >= len check. Now we fail when the path length increases between the two calls.