Add Server screen saves invalid addresses like "." without validation

Short description
The "Add Server" screen lets the player save a server address that can never be valid, such as a single dot ".". The "Done" button stays usable, the entry is saved, and the error only appears later when trying to join.

Steps to reproduce

1. Open Multiplayer > Add Server.

2. Enter any name and set the Server Address field to ".".

3. Click "Done". The entry is saved without any warning.

4. Try to join the new entry.

Expected result
Addresses that are syntactically invalid (for example only punctuation, such as ".") are rejected or flagged when saving, for example by disabling "Done" or by showing a warning on the field.

I am not asking for a DNS or reachability check at save time. Servers can legitimately be offline, not yet resolvable, or on a LAN, so those must stay allowed. Only a format check is requested.

Actual result
The entry is saved. Joining fails with the screen "Failed to connect to the server" / "Unknown host" (shown in my Turkish localization as "Sunucuya bağlanılamadı - Bilinmeyen sunucu"). The message itself is accurate, but the invalid address could have been caught earlier.