fix require_scenario & require_era

previously both were broken:
1) 'require_scenario' was only checked if the scenario was installed
which obviously doesn't make any sense at all.
2) 'require_scenario' was read from the local scenario data instead from
the remote scenario.
3) 'require_era' was only checked when the scenario was not installed,
so people who do have an outated version of the era installed could not
join bacause it assumed require_era=yes in that case.
4) the server tried to read 'require_scenario' from the wrong wml node,
'require_scenario' is an attribute of [scenario] and not of savefile
toplevel.

(cherry-picked from commit eec8b67)

src/game_initialization/lobby_data.cpp

@@ -259,17 +259,20 @@ game_info::game_info(const config& game, const std::vector<std::string>& install
 
 	if(!game["mp_era"].empty()) {
 		const config& era_cfg = game_config.find_child("era", "id", game["mp_era"]);
+		const bool require = game["require_era"].to_bool(true);
 		if(era_cfg) {
 			era = era_cfg["name"].str();
 			era_short = era_cfg["short_name"].str();
 			if(era_short.empty()) {
 				era_short = make_short_name(era);
 			}
 
-			ADDON_REQ result = check_addon_version_compatibility(era_cfg, game);
-			addons_outcome = std::max(addons_outcome, result); // Elevate to most severe error level encountered so far
+			if(require) {
+				ADDON_REQ result = check_addon_version_compatibility(era_cfg, game);
+				addons_outcome = std::max(addons_outcome, result); // Elevate to most severe error level encountered so far
+			}
 		} else {
-			have_era = !game["require_era"].to_bool(true);
+			have_era = !require;
 			era = game["mp_era_name"].str();
 			era_short = make_short_name(era);
 			verified = false;
@@ -339,6 +342,7 @@ game_info::game_info(const config& game, const std::vector<std::string>& install
 	if(!game["mp_scenario"].empty() && game["mp_campaign"].empty()) {
 		// Check if it's a multiplayer scenario
 		const config* level_cfg = &game_config.find_child("multiplayer", "id", game["mp_scenario"]);
+		const bool require = game["require_scenario"].to_bool(false);
 
 		// Check if it's a user map
 		if(!*level_cfg) {
@@ -371,11 +375,14 @@ game_info::game_info(const config& game, const std::vector<std::string>& install
 				}
 			}
 
-			if((*level_cfg)["require_scenario"].to_bool(false)) {
+			if(require) {
 				ADDON_REQ result = check_addon_version_compatibility((*level_cfg), game);
 				addons_outcome = std::max(addons_outcome, result); // Elevate to most severe error level encountered so far
 			}
 		} else {
+			if(require) {
+				addons_outcome = std::max(addons_outcome, NEED_DOWNLOAD); // Elevate to most severe error level encountered so far
+			}
 			scenario = formatter() << make_game_type_marker(_("scenario_abbreviation^S"), true) << game["mp_scenario_name"].str();
 			info_stream << scenario;
 			verified = false;

src/server/server.cpp

@@ -1553,8 +1553,11 @@ void server::handle_player_in_game(socket_ptr socket, std::shared_ptr<simple_wml
 		// Update the game's description.
 		// If there is no shroud, then tell players in the lobby
 		// what the map looks like
+		const simple_wml::node& s = *wesnothd::game::starting_pos(g.level().root());
+		// fixme: the hanlder of [store_next_scenario] below searches for 'mp_shroud' in [scenario]
+		//        at least of the these cosed is likely wrong.
 		if(!data["mp_shroud"].to_bool()) {
-			desc.set_attr_dup("map_data", (*wesnothd::game::starting_pos(data.root()))["map_data"]);
+			desc.set_attr_dup("map_data", s["map_data"]);
 		}
 
 		if(const simple_wml::node* e = data.child("era")) {
@@ -1563,7 +1566,7 @@ void server::handle_player_in_game(socket_ptr socket, std::shared_ptr<simple_wml
 			}
 		}
 
-		if(data.attr("require_scenario").to_bool(false)) {
+		if(s["require_scenario"].to_bool(false)) {
 			desc.set_attr("require_scenario", "yes");
 		}
 
@@ -1658,7 +1661,7 @@ void server::handle_player_in_game(socket_ptr socket, std::shared_ptr<simple_wml
 			}
 		}
 
-		if(data.attr("require_scenario").to_bool(false)) {
+		if(s["require_scenario"].to_bool(false)) {
 			desc.set_attr("require_scenario", "yes");
 		}