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/AI/SmartScripts/SmartAI.cpp

@@ -230,6 +230,8 @@ void SmartAI::EndPath(bool fail)
                 for (GroupReference* groupRef = group->GetFirstMember(); groupRef != nullptr; groupRef = groupRef->next())
                 {
                     Player* groupGuy = groupRef->GetSource();
+                    if (!groupGuy->IsInMap(player))
+                        continue;
 
                     if (!fail && groupGuy->IsAtGroupRewardDistance(me) && !groupGuy->HasCorpse())
                         groupGuy->AreaExploredOrEventHappens(mEscortQuestID);
@@ -386,8 +388,7 @@ bool SmartAI::IsEscortInvokerInRange()
                 for (GroupReference* groupRef = group->GetFirstMember(); groupRef != nullptr; groupRef = groupRef->next())
                 {
                     Player* groupGuy = groupRef->GetSource();
-
-                    if (me->GetDistance(groupGuy) <= SMART_ESCORT_MAX_PLAYER_DIST)
+                    if (groupGuy->IsInMap(player) && me->GetDistance(groupGuy) <= SMART_ESCORT_MAX_PLAYER_DIST)
                         return true;
                 }
             }