Add a new test for OpenFile function from windows.cfg.

It is here as a reminder for a TODO. When used with OF_EXIST flag, the function OpenFile doesn't return a handle and thus, doesn't leak any resource.
As cppcheck doesn't support such feature yet, it's added a TODO not to be forgotten for later fix when cppcheck supports this.

Also added a naive check, just to ensure the OpenFile check doesn't get broken when adding support for OF_EXIST.