GUIBaseContext :: doAfterUndock - Post-event handler for Undocking events

The GUI event is signaled, when a docking window is undocked from its docking area(GEV_Undock event). The handler allows e.g. changing the layout to the undocking (floating) view.

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 an error has no effect for post-events.
• 0 (ok) - Event handler terminated successfully.