Add locking around stats record fetch to resolve Mantis 7793.

OpenSim/Framework/Monitoring/StatsManager.cs

@@ -262,6 +262,8 @@ namespace OpenSim.Framework.Monitoring
         {
             OSDMap map = new OSDMap();
 
+            lock (RegisteredStats)
+            {
                 foreach (string catName in RegisteredStats.Keys)
                 {
                     // Do this category if null spec, "all" subcommand or category name matches passed parameter.
@@ -290,6 +292,7 @@ namespace OpenSim.Framework.Monitoring
                     }
                     map.Add(catName, contMap);
                 }
+            }
 
             return map;
         }