CLOSE_CB
Called just before a dialog is hidden due to some action over it - for example, double clicking the system's menu box, usually located to the left in the title bar.
Callback
int function(Ihandle *ih); [in C] elem:close_cb() -> (ret: number) [in Lua]
ih: identifies the element that activated the event.
Return: if IUP_IGNORE, it prevents the dialog from being hidden. If you destroy the dialog in this callback, you must return IUP_IGNORE. IUP_CLOSE will be processed.