Partial revert of 15a207f, which was causing issues (ref #4943 and #19768). Instead, fix the underlying issue from 15a207f one level further down - Unit::getAttackerForHelper() shouldn't return units that we aren't in combat with (victim can be such a unit for players/player pets, which can startattack from a distance without entering combat). (#19814)

Fixes the following issues:
- Player pets would aggro neutral mobs as soon as they start autocasting (Imp's Firebolt) if they're in react range (due to victim != null, autocast counts as autoattack and sets victim)
- Neutral mobs would randomly evade when aggro switched between targets.

Closes #19768, #19485 and #10921.

(from PR #19814)

(cherry picked from commit 69fd6245dc)

src/server/game/Entities/Creature/Creature.cpp

@@ -2425,14 +2425,9 @@ bool Creature::_IsTargetAcceptable(Unit const* target) const
     Unit const* targetVictim = target->getAttackerForHelper();
 
     // if I'm already fighting target, or I'm hostile towards the target, the target is acceptable
-    if (GetVictim() == target || IsHostileTo(target))
+    if (IsInCombatWith(target) || IsHostileTo(target))
         return true;
 
-    // a player is targeting me, but I'm not hostile towards it, and not currently attacking it, the target is not acceptable
-    // (players may set their victim from a distance, and doesn't mean we should attack)
-    if (target->GetTypeId() == TYPEID_PLAYER && targetVictim == this)
-        return false;
-
     // if the target's victim is friendly, and the target is neutral, the target is acceptable
     if (targetVictim && IsFriendlyTo(targetVictim))
         return true;

src/server/game/Entities/Unit/Unit.cpp

@@ -5635,13 +5635,22 @@ void Unit::_removeAttacker(Unit* pAttacker)
 
 Unit* Unit::getAttackerForHelper() const                 // If someone wants to help, who to give them
 {
-    if (GetVictim() != NULL)
-        return GetVictim();
+    if (Unit* victim = GetVictim())
+        if (!IsControlledByPlayer() || IsInCombatWith(victim) || victim->IsInCombatWith(this))
+            return victim;
 
     if (!m_attackers.empty())
         return *(m_attackers.begin());
 
-    return NULL;
+    if (Player* owner = GetCharmerOrOwnerPlayerOrPlayerItself())
+    {
+        HostileRefManager& refs = owner->getHostileRefManager();
+        for (Reference<Unit, ThreatManager> const& ref : refs)
+            if (Unit* hostile = ref.GetSource()->GetOwner())
+                return hostile;
+    }
+
+    return nullptr;
 }
 
 bool Unit::Attack(Unit* victim, bool meleeAttack)