The modified patch prevents entity loading off the main thread when
entities are initially loaded.
However, the initial loading of an entity is not the only time the
Entity#readAdditionalSaveData method is called. Commands like /data also
invoke the method (through Entity#load) to update an entities data
without completely re-creating it.
This however breaks with the current patch, as the patch moves parts of
the entity lookup for persistent anger deserialisation into the first
tick of an entity (which obviously is only called once and hence not
re-run when an already ticking entity is modified as laid out above).
This change actively runs the now split logic for deserialisation again
if the entity has already ticked its first tick. This way, initial
deserialisation is still split into one off thread and the first tick
parts, but following main thread deserialisations can happen completely
inside Entity#readAdditionalSaveData is called.
