Fix: [Network] don't rebuild the host-list during iterating the list (#9240)

Additionally, only rebuild it when we added a new manual server,
as otherwise it is a noop anyway.

src/network/network.cpp

@@ -701,7 +701,6 @@ NetworkGameList *NetworkAddServer(const std::string &connection_string, bool man
 		ClearGRFConfigList(&item->info.grfconfig);
 		item->info.server_name = connection_string;
 
-		NetworkRebuildHostList();
 		UpdateNetworkGameWindow();
 
 		NetworkQueryServer(connection_string);

src/network/network_gui.cpp

@@ -830,6 +830,7 @@ public:
 		if (!StrEmpty(str)) {
 			strecpy(_settings_client.network.connect_to_ip, str, lastof(_settings_client.network.connect_to_ip));
 			NetworkAddServer(str);
+			NetworkRebuildHostList();
 		}
 	}