If the viewer has already rezzed any attachments itself, then ignore the simulator-side rez attachments call.

This is a further effort to reduce v3 viewer race conditions where this call may clash with the viewer signalling attachment wearing from its current outfit folder.

OpenSim/Region/Framework/Interfaces/IAttachmentsModule.cs

@@ -53,6 +53,10 @@ namespace OpenSim.Region.Framework.Interfaces
         /// RezAttachments. This should only be called upon login on the first region.
         /// Attachment rezzings on crossings and TPs are done in a different way.
         /// </summary>
+        /// <remarks>
+        /// This is only actually necessary for viewers which do not have a current outfit folder (these viewers make
+        /// their own attachment calls on login) and agents which have attachments but no viewer (e.g. NPCs).
+        /// </remarks>
         /// <param name="sp"></param>
         void RezAttachments(IScenePresence sp);