Log if a world unload is requested even though allowWorldUnloading is set to false

Signed-off-by: Ross Allan <rallanpcl@gmail.com>
Remove unneeded multiverseWorld field from world.

Signed-off-by: Ross Allan <rallanpcl@gmail.com>
Fix Revamp NPE after a world unloads

Signed-off-by: Ross Allan <rallanpcl@gmail.com>