* Introduce an IsAttachment property on the group level (which just returns false if the group is already deleted)

* This is to avoid repetitive null checks - I'm beginning to think that blasting away the root part on object deletion is actually a bad move.  Perhaps we should leave it around 
and let the client ignore any superfluous packets (which it may well do anyway), since we're constantly exposing a race condition

OpenSim/Region/Environment/Modules/World/Archiver/ArchiveWriteRequestPreparation.cs

@@ -276,7 +276,7 @@ namespace OpenSim.Region.Environment.Modules.World.Archiver
                 {
                     SceneObjectGroup sceneObject = (SceneObjectGroup)entity;
                     
-                    if (sceneObject.RootPart != null && !sceneObject.RootPart.IsAttachment)
+                    if (!sceneObject.IsDeleted && !sceneObject.IsAttachment)
                         sceneObjects.Add((SceneObjectGroup)entity);
                 }
             }

OpenSim/Region/Environment/Scenes/SceneObjectGroup.cs

@@ -94,6 +94,26 @@ namespace OpenSim.Region.Environment.Scenes
         /// </summary>
         public bool HasGroupChanged = false;
         
+        /// <value>
+        /// Is this scene object acting as an attachment?
+        /// 
+        /// We return false if the group has already been deleted.
+        ///  
+        /// TODO: At the moment set must be done on the part itself.  There may be a case for doing it here since I
+        /// presume either all or no parts in a linkset can be part of an attachment (in which
+        /// case the value would get proprogated down into all the descendent parts).
+        /// </value>
+        public bool IsAttachment
+        {
+            get
+            {
+                if (!IsDeleted)
+                    return m_rootPart.IsAttachment;
+                
+                return false;
+            }
+        }
+
         public float scriptScore = 0f;
 
         private Vector3 lastPhysGroupPos;