GUIBaseContext :: doBeforeOrder - Pre-event handler before ordering a collection by column

The handler handles the GEV_Order GUI event. The event is fired before ordering a tree, list or table control. When the event is fired, list entries are not yet ordered.

The handler should return one of the following return codes:

• -1 (not handled) - the event handler will be removed from the handler list and is not called anymore.
• 1 (error) - Returning 1 suppresses ordering list entries.
• 0 (ok) - Event handler terminated successfully.