Core/Spells: Possible crash fix

Get Unit target with the proper method instead of retrieving Object target and then casting it to Unit, possible dereferencing NULL.
Updates #11560

src/server/game/Spells/Spell.cpp

@@ -3020,7 +3020,7 @@ void Spell::cast(bool skipCheck)
         if (this->GetSpellInfo()->DmgClass != SPELL_DAMAGE_CLASS_NONE)
             if (Pet* playerPet = playerCaster->GetPet())
                 if (playerPet->IsAlive() && playerPet->isControlled() && (m_targets.GetTargetMask() & TARGET_FLAG_UNIT))
-                    playerPet->AI()->OwnerAttacked(m_targets.GetObjectTarget()->ToUnit());
+                    playerPet->AI()->OwnerAttacked(m_targets.GetUnitTarget());
     }
 
     SetExecutedCurrently(true);