Core/Misc: Fix various crashes, also related to multithreading (#19012)

* When iterating groups we have to either do it not in multithreaded context (map updates) or start with checking maps (they are guaranteed to change in single thread update).
* Properly clear ComboPoint references on player remove 
* remove some possible references item may have when it is deleted during save. 
* Also clear all hostile references when unit is removed from map.

src/server/game/Entities/GameObject/GameObject.cpp

@@ -613,7 +613,7 @@ void GameObject::Update(uint32 diff)
                         {
                             Group* group = sGroupMgr->GetGroupByGUID(lootingGroupLowGUID);
                             if (group)
-                                group->EndRoll(&loot);
+                                group->EndRoll(&loot, GetMap());
                             m_groupLootTimer = 0;
                             lootingGroupLowGUID = 0;
                         }
@@ -1331,7 +1331,7 @@ void GameObject::Use(Unit* user)
 
                 if (itr->second)
                 {
-                    if (Player* ChairUser = ObjectAccessor::FindPlayer(itr->second))
+                    if (Player* ChairUser = ObjectAccessor::GetPlayer(*this, itr->second))
                     {
                         if (ChairUser->IsSitState() && ChairUser->GetStandState() != UNIT_STAND_STATE_SIT && ChairUser->GetExactDist2d(x_i, y_i) < 0.1f)
                             continue;        // This seat is already occupied by ChairUser. NOTE: Not sure if the ChairUser->GetStandState() != UNIT_STAND_STATE_SIT check is required.