Core/Scripting: Kill pending unit events when swapping AI's

(cherry picked from commit 851c73b3e4)

src/server/game/Scripting/ScriptMgr.cpp

@@ -368,6 +368,8 @@ class CreatureGameObjectScriptRegistrySwapHooks
     // Hook which is called before a creature is swapped
     static void UnloadStage1(Creature* creature)
     {
+        creature->m_Events.KillAllEvents(true);
+
         if (creature->IsCharmed())
             creature->RemoveCharmedBy(nullptr);