Fix #1351 - Server ignores only-reg if in "none" auth mode.

When in none auth mode, registered users don't exist; hence the setting
makes the game impossible to join.

Normally the setting would be greyed out when the user is unregistered,
but commit 475c54bf introduced a new edge case where the stored setting
would apply to the field even if the user is unregistered, making the
setting possible to apply in no-reg mode. Regardless, any client could
have done this, not just the default cockatrice.

The server side fix should prevent all issues in the future.

servatrice/src/servatrice.h

@@ -136,6 +136,7 @@ public:
     bool initServer();
     QString getServerName() const { return serverName; }
     QString getLoginMessage() const { QMutexLocker locker(&loginMessageMutex); return loginMessage; }
+    bool permitUnregisteredUsers() const { return authenticationMethod != AuthenticationNone; }
     bool getGameShouldPing() const { return true; }
     bool getClientIdRequired() const { return clientIdRequired; }
     bool getRegOnlyServer() const { return regServerOnly; }