CLOSE_CB
Called just before a dialog is closed when the user clicks the close button of the title bar or an equivalent action.
Callback
int function(Ihandle *ih);ih: identifies the element that activated the event.
Returns: if IUP_IGNORE, it prevents the dialog from being closed. If you destroy the dialog in this callback, you must return IUP_IGNORE. IUP_CLOSE will be processed.