wesnothd: exception safety fix

This fixes crash in response to server_shutdown exception getting
thrown, as well as any other exception, that happens if there are any
players logged on.

src/server/wesnothd/server.cpp

@@ -1069,7 +1069,9 @@ template<class SocketPtr> void server::handle_player(boost::asio::yield_context
 	assert(inserted);
 
 	BOOST_SCOPE_EXIT_ALL(this, &player) {
-		remove_player(player);
+		if(!destructed) {
+			remove_player(player);
+		}
 	};
 
 	async_send_doc_queued(socket, games_and_users_list_);
@@ -1368,7 +1370,7 @@ void server::cleanup_game(game* game_ptr)
 
 	// Send a diff of the gamelist with the game deleted to players in the lobby
 	simple_wml::document diff;
-	if(make_delete_diff(*gamelist, "gamelist", "game", game_ptr->description(), diff)) {
+	if(!destructed && make_delete_diff(*gamelist, "gamelist", "game", game_ptr->description(), diff)) {
 		send_to_lobby(diff);
 	}
 

src/server/wesnothd/server.hpp

@@ -37,6 +37,13 @@ class server : public server_base
 public:
 	server(int port, bool keep_alive, const std::string& config_file, std::size_t, std::size_t);
 
+	// We keep this flag for coroutines. Since they get their stack unwinding done after player_connections_
+	// is already destroyed they need to know to avoid calling remove_player() on invalid iterators.
+	bool destructed = false;
+	~server() {
+		destructed = true;
+	}
+
 private:
 	void handle_new_client(socket_ptr socket);
 	void handle_new_client(tls_socket_ptr socket);
@@ -118,25 +125,6 @@ class server : public server_base
 
 	std::mt19937 die_;
 
-	player_connections player_connections_;
-
-	std::deque<std::shared_ptr<game>> games() const
-	{
-		std::deque<std::shared_ptr<game>> result;
-
-		for(const auto& iter : player_connections_.get<game_t>()) {
-			if(result.empty() || iter.get_game() != result.back()) {
-				result.push_back(iter.get_game());
-			}
-		}
-
-		if(!result.empty() && result.front() == nullptr) {
-			result.pop_front();
-		}
-
-		return result;
-	}
-
 #ifndef _WIN32
 	/** server socket/fifo. */
 	std::string input_path_;
@@ -192,6 +180,25 @@ class server : public server_base
 
 	metrics metrics_;
 
+	player_connections player_connections_;
+
+	std::deque<std::shared_ptr<game>> games() const
+	{
+		std::deque<std::shared_ptr<game>> result;
+
+		for(const auto& iter : player_connections_.get<game_t>()) {
+			if(result.empty() || iter.get_game() != result.back()) {
+				result.push_back(iter.get_game());
+			}
+		}
+
+		if(!result.empty() && result.front() == nullptr) {
+			result.pop_front();
+		}
+
+		return result;
+	}
+
 	boost::asio::steady_timer dump_stats_timer_;
 	void start_dump_stats();
 	void dump_stats(const boost::system::error_code& ec);