Restored Warmonger's changes to artifacts system.

They will be subject of my further work, along with next part of bonus system.

server/NetPacksServer.cpp

@@ -166,7 +166,7 @@ bool TradeOnMarketplace::applyGh( CGameHandler *gh )
 	case CREATURE_EXP:
 		return gh->sacrificeCreatures(m, hero, r1, val);
 	case ARTIFACT_EXP:
-		return gh->sacrificeArtifact(m, hero, r1);
+		return gh->sacrificeArtifact(m, hero, hero->getArtAtPos(r1));
 	default:
 		COMPLAIN_AND_RETURN("Unknown exchange mode!");
 	}