[GREENFOOT-670] Deleting the current world class causes exceptions
If you delete the current world class (i.e. the one that instantiates by default), you will get exceptions when Greenfoot later tries to use the currentWorld field in GreenfootStage. The way to solve this might be to listen for class deletions in GreenfootStage, and null out currentWorld if we see that it is the class that is being deleted.
- Issue type: Task
- Priority: Medium