Core/AI: Add some checks to catch if the AI changes mid-update for players.

Port From (https://github.com/TrinityCore/TrinityCore/commit/1015f307041b25b47a9bb4bc76ac4ed78c49d735)

Source/Game/Entities/Unit/Unit.Fields.cs

@@ -33,6 +33,7 @@ namespace Game.Entities
         //AI
         protected UnitAI i_AI;
         protected UnitAI i_disabledAI;
+        bool m_aiLocked;
 
         //Movement
         protected float[] m_speed_rate = new float[(int)UnitMoveType.Max];