[Spell][Mage] Arcane Power

Originally from: https://github.com/NoReturn

Mage's spell Arcane Power is incorrectly handled as a debuff, means the
player gets the benefit from it but the icon is shown in the debuff
section of the GUI and also makes the buff immune to enemy
dispells/spell steals/etc.

Hacky fix

src/game/Object/SpellMgr.cpp

@@ -848,6 +848,8 @@ bool IsPositiveEffect(SpellEntry const* spellproto, SpellEffectIndex effIndex)
                     switch (spellproto->EffectMiscValue[effIndex])
                     {
                         case SPELLMOD_COST:                 // dependent from bas point sign (negative -> positive)
+                        if(spellproto->Id == 12042)         // Arcane Power
+                                break;
                             if (spellproto->CalculateSimpleValue(effIndex) > 0)
                                 { return false; }
                             break;