GUIBaseContext :: doBeforeSaveData - Pre-event handler for Cancel action

The handler handles the DEV_Save data event in a Save action. When the event is fired, an instance in the property handle not yet stored and can be accessed. The event handler may prevent data from being stored by returning true.

The handler should return one of the following values:

• -1 (not handled) - the event handler will be removed from the handler list and is not called anymore.
• 1 (refuse) - Requested action will not be executed.
• 0 (ok) - Action is permitted to be executed.