Initializes the CShellManager object.
If you call CWinAppEx::GetShellManager, the default implementation of that method calls InitShellManager.
If your application already has a shell manager and you call InitShellManager, your application raises an ASSERT failure. Therefore, do not call InitShellManager if you create a CShellManager object directly. If you are not using a custom CShellManager, use GetShellManager to create a CShellManager object.