Fix NPC shutdown crash (#2971)

Co-authored-by: Metal Gear Sloth <metalgearsloth@gmail.com>

Content.Server/AI/Utility/AiLogic/UtilityAI.cs

@@ -137,6 +137,8 @@ namespace Content.Server.AI.Utility.AiLogic
         {
             var currentOp = CurrentAction?.ActionOperators.Peek();
             currentOp?.Shutdown(Outcome.Failed);
+            CurrentAction?.Shutdown();
+            CurrentAction = null;
         }
 
         public void MobStateChanged(MobStateChangedMessage message)