- The 2nd parameter is already passed in user-mode by GetThreadDesktop().
It is then used by NtUserGetThreadDesktop() as a fallback for console
threads.
- Lookup and validate the thread by using the IntTID2PTI() helper.
- Don't reference the desktop with too many access rights.
- Get rid of the old-school DECLARE_RETURN() & co. macros.
Co-authored-by: Hermès Bélusca-Maïto <hermes.belusca-maito@reactos.org>