[GREENFOOT-771] Save the world can happen when it probably shouldn't

Our rule used to be that if you have hit run, you can no longer save the world until you reset the world. However, in 3.5.0rc3 this restriction is not in place. You can run, pause, make new objects and save the world, and the new objects will be succesfully recorded for next time. Similarly, you can run, pause, drag a saved object to a new position, save the world, and that position will be its start position in future.

It's not terrible as there are no exceptions and it's not an unreasonable outcome, but we may still want to prohibit it as it is a big strange to be able to do it.

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Issue metadata

• Issue type: Task
• Priority: Medium