Can't connect to LAN games using Direct Connect if offline

When offline, joining LAN games works from the server list, but entering the IP address in the Direct Connect box will give an authentication error. This is an issue because some networks don't handle multicast over WiFi properly, meaning LAN games won't appear in the server list.

Steps to reproduce:

1. Disable your network connection

2. Open two instances of Minecraft

3. On one instance, create a world and Open to LAN

4. On the other instance, click Direct Connect in the Multiplayer menu, and join localhost:<port>

5. The connection will fail, stating that the authentication servers are unavailable

6. Go back to the server list, and join the game from the server list

7. The connection will succeed. Note that if both instances are launched on the same account it will fail with "that username is taken," this is expected behavior.