When teleporting, the spawn position packet will contain the
old position. Then the following tracking update will send a
teleport packet, but the client will lerp the position change
over 3 ticks. However, the client does not tick entities in
unloaded chunks - resulting in the lerp never occuring.
We fix this by sending the current position in the spawn packet.
The delta position packet instructs the client to update
the entity position by a position difference. However, this position
difference is relative to the last position in the entity tracker
state, not the last position which has been sent to the player. As
a result, if the last position the player has recorded is different
than the one stored in the entity tracker (which occurs when a new
player is added to an existing entity tracker state) then the sent
position difference will cause a position desync for the client.
We can resolve this problem by either tracking the last position
sent per-player, or by simply resetting the last sent position
in the entity tracker state every time a new player is added.
Resetting the last sent position every time a new player is
added to the tracker is just easier to do, so that is what
this patch does.
