Override this function to handle the WM_NOTIFY CDN_TYPECHANGE message.
The notification message is sent when the user selects a new file type from the list of file types in the Open or Save As dialog box.
Notification is sent only if the dialog box was created with the OFN_EXPLORER style. For more information about the notification, see CDN_TYPECHANGE. For information about the OFN_EXPLORER style, see the OPENFILENAME structure and Open and Save As Dialog Boxes.