[Lazarus] tFileOpen Action, Is it possible to cancel the dialog...

[Wildfire]

Just started messing about with the standard actions in Lazarus and came 
across a minor problem.

Is in possible to cancel the dialog in the BeforeExecute event, my plan was 
to ask the user to save the current file (Yes/No/Cancel) before opening 
another, problem is I don't know how to cancel the Dialog if the User 
selects Cancel.

My apologies if I'm missing something glaringly obvious but I've never used 
actions before and although I can work around it I was just hoping I could 
do it within the actions events themselves.