Fix issue with the quit packet being stuck int he queue and a one packet delay.

Also fix semaphore excetion caused by enqueueing while dequque is taking place.

OpenSim/Region/ClientStack/Linden/UDP/LLUDPServer.cs

@@ -1606,10 +1606,16 @@ namespace OpenSim.Region.ClientStack.LindenUDP
                 else
                     res = m_lowQueue.Dequeue();
 
-                if (m_highQueue.Count == 0 || m_lowQueue.Count == 0)
+                if (m_highQueue.Count == 0 && m_lowQueue.Count == 0)
                     return true;
 
+                try
+                {
                     m_s.Release();
+                }
+                catch
+                {
+                }
 
                 return true;
             }