Save disconnect frame in the GameInformation

This information is useful to infer a winner in case the winstate is
unknown.

OpenRA.Game/GameInformation.cs

@@ -179,6 +179,9 @@ namespace OpenRA
 			/// <summary>The time when this player won or lost the game.</summary>
 			public DateTime OutcomeTimestampUtc;
 
+			/// <summary>The frame at which this player disconnected.</summary>
+			public int DisconnectFrame;
+
 			#endregion
 		}
 	}