Prevent acks from being appended to viewer effect packets, since

that has been known to cause an exception in libomv ^^

OpenSim/Region/ClientStack/LindenUDP/LLPacketHandler.cs

@@ -248,6 +248,13 @@ namespace OpenSim.Region.ClientStack.LindenUDP
 
         private void AddAcks(ref Packet packet)
         {
+			// This packet type has shown to have issues with
+			// acks being appended to the payload, just don't send
+			// any with this packet type until libsl is fixed.
+			//
+			if(packet is libsecondlife.Packets.ViewerEffectPacket)
+				return;
+
             // Add acks to outgoing packets
             //
             if (m_PendingAcks.Count > 0)