Fix additional damage attribute reducing damage

[Yentis]

No description provided.

[exjam]

If we want to keep this as close as possible to the original official source CCal functions

		if ( FLAG_ING_DUMMY_DAMAGE & pATK->GetIngDurationStateFLAG() ) {
			iDamage += (int)( iDamage * SKILL_POWER( pATK->GetIngDurationStateSKILL( ING_DUMMY_DAMAGE ) ) / 100.f );
			// iDamage |= DMG_BIT_DUMMY;
		}

It seems what we should have done is:
damage += damage * attacker.get_additional_damage_multipler();

[exjam]

Thanks!