Update ClientEventHandler.java

Added null check on UUIDs.
This should fix NullPointerEexceptions when dealing with FakeClientPlayers like BiblioCraft Armorstands.

I noticed this when making a custom armorstand (these need fake client players, because some armors like Thaumcraft's Fortress Armor check a players inventory to base certain elements of their render on).
Installed BiblioCraft and noticed the same exception, checked your code and found that a simple !=null should fix this^^