Lock the object queue when dequeueing

OpenSim/Region/Framework/Scenes/SceneViewer.cs

@@ -66,6 +66,8 @@ namespace OpenSim.Region.Framework.Scenes
         }
 
         public void SendPrimUpdates()
+        {
+            lock(m_pendingObjects)
             {
                 if (m_pendingObjects == null)
                 {
@@ -75,7 +77,7 @@ namespace OpenSim.Region.Framework.Scenes
 
                         foreach (EntityBase e in m_presence.Scene.Entities)
                         {
-                        if (e is SceneObjectGroup)
+                            if (e != null && e is SceneObjectGroup)
                                 m_pendingObjects.Enqueue((SceneObjectGroup)e);
                         }
                     }
@@ -169,6 +171,7 @@ namespace OpenSim.Region.Framework.Scenes
                     }
                 }
             }
+        }
 
         public void Reset()
         {