Scripts/Icecrown Citadel: Professor Putricide - fixed Expunged Gas damage formula

Closes #6396

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

@@ -7475,8 +7475,8 @@ bool Unit::HandleAuraProc(Unit* victim, uint32 damage, Aura* triggeredByAura, Sp
                     uint32 stack = triggeredByAura->GetStackAmount();
                     int32 const mod = (GetMap()->GetSpawnMode() & 1) ? 1500 : 1250;
                     int32 dmg = 0;
-                    for (uint8 i = 1; i < stack; ++i)
-                        dmg += mod * stack;
+                    for (uint8 i = 1; i <= stack; ++i)
+                        dmg += mod * i;
                     if (Unit* caster = triggeredByAura->GetCaster())
                         caster->CastCustomSpell(70701, SPELLVALUE_BASE_POINT0, dmg);
                     break;