If a Game with empty filename happens to be deleted (e.g. during sync merge), it will accidentally delete the *entire* Games folder due to its fileURL being “Games/[empty]”.
To prevent this, we now explicitly check that a Game’s identifier isn’t empty AND that that Game.fileURL doesn’t point to a directory before deleting local files.
When Core Data detects a duplicate entry, it deletes the previous entry. This caused Delta to delete the associated ROM and Save State files. Now, there is a check in prepareForDeletion to make sure the object being deleted is not simply being replaced by a newer entry during a merge.
