Override updateLeashedState() function in EntityNPCInterface.

NPCs can't be leashed anyway. This should avoid the "does not know how to add entity" crash with NPCs.

src/main/java/noppes/npcs/entity/EntityNPCInterface.java

@@ -1817,4 +1817,6 @@ public abstract class EntityNPCInterface extends EntityCreature implements IEnti
 	{
 		this.display.modelType = val;
 	}
+
+	protected void updateLeashedState(){}
 }