Disable 1 human versus bots games

Changed the Server.LockBots setting to Server.DisableSinglePlayer.

If the setting is enabled, and there is only one client in the server,
the game won't start.

OpenRA.Game/Network/Session.cs

@@ -196,6 +196,7 @@ namespace OpenRA.Network
 			public bool ShortGame = true;
 			public bool AllowVersionMismatch;
 			public string GameUid;
+			public bool DisableSingleplayer;
 
 			public static Global Deserialize(MiniYaml data)
 			{