It's been seen on Windows 11 (22H2) Build 22621.3155 that NtCreateFile
will return the OBJECT_NAME_INVALID error code with certain path names.
The path name we saw this with started with `C:Users` (rather than
`C:\Users`) and also contained a `$` character.  This PR updates our
OpenFile wrapper to propagate this error code as `error.BadPathName`
instead of making it `unreachable`.

see https://github.com/marler8997/zigup/issues/114#issuecomment-1994420791