Fix hologram net messages (setScale/setClip)

Net messages can arrive before the entity is initialised.
While there was a queue to accomodate for that, the queue was indexed by
the entity. However, since all non-existant entities become
NULL-Entities, the queue was not working.

This changes the queue to be indexed by the entity index.

Fixes #20
Merge pull request #21 from Xandaros/hologram-scale

Fix hologram net messages (setScale/setClip)