Don't return a replay URL for private games.

The URL wouldn't work anyway.

src/server/common/dbconn.cpp

@@ -125,7 +125,11 @@ std::unique_ptr<simple_wml::document> dbconn::get_game_history(int player_id, in
 "  IFNULL(era.ID, '') as ERA_ID, "
 "  IFNULL(GROUP_CONCAT(distinct mods.NAME, '') as MODIFICATION_NAMES, "
 "  IFNULL(GROUP_CONCAT(distinct mods.ID), '') as MODIFICATION_IDS, "
-"  concat('https://replays.wesnoth.org/', substring(game.INSTANCE_VERSION, 1, 4), '/', year(game.END_TIME), '/', lpad(month(game.END_TIME), 2, '0'), '/', lpad(day(game.END_TIME), 2, '0'), '/', game.REPLAY_NAME) as REPLAY_URL "
+"  case "
+"  when game.PUBLIC = 1 "
+"  then concat('https://replays.wesnoth.org/', substring(game.INSTANCE_VERSION, 1, 4), '/', year(game.END_TIME), '/', lpad(month(game.END_TIME), 2, '0'), '/', lpad(day(game.END_TIME), 2, '0'), '/', game.REPLAY_NAME) "
+"  else '' "
+"  end as REPLAY_URL "
 "from "+db_game_info_table_+" game "
 "inner join "+db_game_player_info_table_+" player "
 "   on exists "