SystemTools: Fix Windows app exec alias layout

Fix the layout added by commit 025a4951 (SystemTools: Add Windows app
exec alias support to ReadSymlink, 2021-10-28) to match this reference:

  https://www.tiraniddo.dev/2019/09/overview-of-windows-execution-aliases.html



Reported-by: Yuriy O'Donnell <yuriy.odonnell@epicgames.com>