Fix: Rare timing issue on first-use causing duplicate naming config

src/NzbDrone.Core/Organizer/NamingConfigService.cs

@@ -19,11 +19,19 @@ namespace NzbDrone.Core.Organizer
         {
             var config = _repository.SingleOrDefault();
 
+            if (config == null)
+            {
+                lock (_repository)
+                    {
+                    config = _repository.SingleOrDefault();
+
                     if (config == null)
                     {
                         _repository.Insert(NamingConfig.Default);
                         config = _repository.Single();
                     }
+                }
+            }
 
             return config;
         }