Completion of 45a0edb: Index based entity list iteration
As saving a leashed entity may add a new entity (a leash hitch) to the current world, the usage of an iterator, to go through the list of entities in a chunk slice, is not safe here anymore. The iterator should throw a ConcurrentModificationException in that case, as the list was modified during iteration. Interestingly it didnt do that in my tests, but it should