[rencro]

I have not compiled this myself but perhaps something like this may work:

if(IsClient()) {
		const ItemInst *wpn = CastToClient()->GetInv().GetItem(MainPrimary);
		bool havePiercer = true;
		if(!wpn || (wpn->GetItem()->ItemType != ItemType1HPiercing)){
			havePiercer = false;
		}
		if(wpn->GetItem()->ItemType == ItemType2HPiercing || havePiercer == true){
			havePiercer = true;
		}
		if(havePiercer == false) {
			Message_StringID(13, BACKSTAB_WEAPON);
			return;
		}
	}