Vanilla has risk of losing entities by causing them to be
removed from all chunks if they try to move into an unloaded chunk.
This pretty much means high chance this entity will be lost in this scenario.
There is another case that adding an entity to the world can fail if
the chunk isn't loaded.
Lots of the server is designed around addEntity never expecting to fail for these reasons,
nor is it really logical.
This change ensures the chunks are always loaded when entities are
added to the world, or a valid entity moves between chunks.
Hopefully will fix issues #1496 and #1434
