Fix packet size calculation for normal barter shops (#6548)

Fixes #6545

src/map/clif.cpp

@@ -22801,7 +22801,7 @@ void clif_parse_barter_buy( int fd, struct map_session_data* sd ){
 
 	struct PACKET_CZ_NPC_BARTER_PURCHASE* p = (struct PACKET_CZ_NPC_BARTER_PURCHASE*)RFIFOP( fd, 0 );
 
-	uint16 entries = ( p->packetLength - sizeof( struct PACKET_CZ_NPC_EXPANDED_BARTER_PURCHASE ) ) / sizeof( struct PACKET_CZ_NPC_EXPANDED_BARTER_PURCHASE_sub );
+	uint16 entries = ( p->packetLength - sizeof( struct PACKET_CZ_NPC_BARTER_PURCHASE ) ) / sizeof( struct PACKET_CZ_NPC_BARTER_PURCHASE_sub );
 
 	// Empty purchase list
 	if( entries == 0 ){