Fixes U4-5077 doc types with compositions

@nul800sebastiaan  PR with proposed fix for compositions issue.
This get breaks the doctype editor, apparently at some point it gets the contenttype with id -1 (which is null) and then we get null reference errors later on. I think it can be fixed like so: `return ContentTypeItem.ParentId == -1 ? 0 : ContentTypeItem.ParentId;`