Core/AI: Fix crashes caused by charmed Creatures having null AI for 1 map update tick

Port From (https://github.com/TrinityCore/TrinityCore/commit/8c25abca72772e2962bac7f460a567a943388a05)

Source/Game/AI/CoreAI/ScheduledChangeAI.cs

@@ -0,0 +1,43 @@
+/*
+ * Copyright (C) 2012-2020 CypherCore <http://github.com/CypherCore>
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+using Framework.Constants;
+using Game.Entities;
+
+namespace Game.AI
+{
+    class ScheduledChangeAI : CreatureAI
+    {
+        public ScheduledChangeAI(Creature creature) : base(creature) { }
+
+        public override void MoveInLineOfSight(Unit unit) { }
+
+        public override void AttackStart(Unit unit) { }
+
+        public override void JustStartedThreateningMe(Unit unit) { }
+
+        public override void JustEnteredCombat(Unit unit) { }
+
+        public override void UpdateAI(uint diff) { }
+
+        public override void JustAppeared() { }
+
+        public override void EnterEvadeMode(EvadeReason why) { }
+
+        public override void OnCharmed(bool isNew) { }
+    }
+}