-Perform null check and add exception logging in RuleSet.

-Explicitly recognize connection termination on ServerOrder.Deserialize()
-Use explicit exception type for SDL2HardwareCursor failures.

OpenRA.Game/Server/ServerOrder.cs

@@ -30,6 +30,7 @@ namespace OpenRA.Server
 			byte b;
 			switch (b = r.ReadByte())
 			{
+				case 0xbf:
 				case 0xff:
 					Console.WriteLine("This isn't a server order.");
 					return null;