Fix: [Network] clients leaving because of broken connections was not broadcasted (#9238)

The code mixed up "client has quit but we already told everyone"
with "client lost connection, handle this".

Split up those two signals:
- CLIENT_QUIT means we told everyone and the connection is now dead
- CONNECTION_LIST means we should tell everyone we lost a client

src/network/core/core.h

@@ -20,16 +20,17 @@ void NetworkCoreShutdown();
 
 /** Status of a network client; reasons why a client has quit */
 enum NetworkRecvStatus {
-	NETWORK_RECV_STATUS_OKAY,             ///< Everything is okay
-	NETWORK_RECV_STATUS_DESYNC,           ///< A desync did occur
-	NETWORK_RECV_STATUS_NEWGRF_MISMATCH,  ///< We did not have the required NewGRFs
-	NETWORK_RECV_STATUS_SAVEGAME,         ///< Something went wrong (down)loading the savegame
-	NETWORK_RECV_STATUS_CONN_LOST,        ///< The connection is 'just' lost
-	NETWORK_RECV_STATUS_MALFORMED_PACKET, ///< We apparently send a malformed packet
-	NETWORK_RECV_STATUS_SERVER_ERROR,     ///< The server told us we made an error
-	NETWORK_RECV_STATUS_SERVER_FULL,      ///< The server is full
-	NETWORK_RECV_STATUS_SERVER_BANNED,    ///< The server has banned us
-	NETWORK_RECV_STATUS_CLOSE_QUERY,      ///< Done querying the server
+	NETWORK_RECV_STATUS_OKAY,             ///< Everything is okay.
+	NETWORK_RECV_STATUS_DESYNC,           ///< A desync did occur.
+	NETWORK_RECV_STATUS_NEWGRF_MISMATCH,  ///< We did not have the required NewGRFs.
+	NETWORK_RECV_STATUS_SAVEGAME,         ///< Something went wrong (down)loading the savegame.
+	NETWORK_RECV_STATUS_CLIENT_QUIT,      ///< The connection is lost gracefully. Other clients are already informed of this leaving client.
+	NETWORK_RECV_STATUS_MALFORMED_PACKET, ///< We apparently send a malformed packet.
+	NETWORK_RECV_STATUS_SERVER_ERROR,     ///< The server told us we made an error.
+	NETWORK_RECV_STATUS_SERVER_FULL,      ///< The server is full.
+	NETWORK_RECV_STATUS_SERVER_BANNED,    ///< The server has banned us.
+	NETWORK_RECV_STATUS_CLOSE_QUERY,      ///< Done querying the server.
+	NETWORK_RECV_STATUS_CONNECTION_LOST,  ///< The connection is lost unexpectedly.
 };
 
 /** Forward declaration due to circular dependencies */

src/network/core/tcp_admin.cpp

@@ -41,7 +41,7 @@ NetworkAdminSocketHandler::~NetworkAdminSocketHandler()
 NetworkRecvStatus NetworkAdminSocketHandler::CloseConnection(bool error)
 {
 	delete this;
-	return NETWORK_RECV_STATUS_CONN_LOST;
+	return NETWORK_RECV_STATUS_CLIENT_QUIT;
 }
 
 /**

src/network/core/tcp_game.cpp

@@ -48,10 +48,10 @@ NetworkRecvStatus NetworkGameSocketHandler::CloseConnection(bool error)
 		_networking = false;
 		ShowErrorMessage(STR_NETWORK_ERROR_LOSTCONNECTION, INVALID_STRING_ID, WL_CRITICAL);
 
-		return NETWORK_RECV_STATUS_CONN_LOST;
+		return NETWORK_RECV_STATUS_CLIENT_QUIT;
 	}
 
-	return this->CloseConnection(error ? NETWORK_RECV_STATUS_SERVER_ERROR : NETWORK_RECV_STATUS_CONN_LOST);
+	return this->CloseConnection(NETWORK_RECV_STATUS_CONNECTION_LOST);
 }