Problem:
Can't open swapfile when using a device path starting with `//?/`,
because `?` is a reserved char on Widnows.
Solution:
For device UNC paths, replace `//?/UNC/` and `//./UNC/` with `//`.
For other device paths, just strip their prefix (i.e. `//?/`, `//./`).
This aligns swapfile naming for device paths with regular UNC and DOS
paths.
Co-authored-by: Justin M. Keyes <justinkz@gmail.com>