Prevent a race condition between the script engine backup thread and script removal by locking on the script's EventQueue and only proceeding if it's flagged as still running.

Relates to http://opensimulator.org/mantis/view.php?id=7407

OpenSim/Region/ScriptEngine/XEngine/XEngine.cs

@@ -732,8 +732,7 @@ namespace OpenSim.Region.ScriptEngine.XEngine
 
                     // Clear the event queue and abort the instance thread
                     //
-                    instance.ClearQueue();
-                    instance.Stop(0);
+                    instance.Stop(0, true);
 
                     // Release events, timer, etc
                     //
@@ -859,8 +858,6 @@ namespace OpenSim.Region.ScriptEngine.XEngine
                 }
             }
 
-            instances.Clear();
-
             if (saveTime > 0)
                 m_ThreadPool.QueueWorkItem(new WorkItemCallback(this.DoBackup),
                                            new Object[] { saveTime });
@@ -1443,6 +1440,7 @@ namespace OpenSim.Region.ScriptEngine.XEngine
                 m_Scripts.Remove(itemID);
             }
 
+
             instance.ClearQueue();
 
             instance.Stop(m_WaitForEventCompletionOnScriptStop);