if there are no Playable playerrefs in the map, make as many as there are spawnpoints (hack)

OpenRA.Game/Map.cs

@@ -171,6 +171,17 @@ namespace OpenRA
 					throw new InvalidDataException("Map format {0} is not supported.".F(MapFormat));
 			}
 
+			/* hack: make some slots. */
+			if (!Players.Any(p => p.Value.Playable))
+			{
+				int index = 0;
+				foreach (var wp in Waypoints)
+				{
+					var p = new PlayerReference("Multi{0}".F(index++), "Random", false, false) { Playable = true };
+					Players.Add(p.Name, p);
+				}
+			}
+
 			// Smudges
 			foreach (var kv in yaml["Smudges"].Nodes)
 			{

OpenRA.Game/Network/Session.cs

@@ -36,6 +36,7 @@ namespace OpenRA.Network
 			public string Name;
 			public ClientState State;
 			public int Team;
+			public int Slot;	//	which slot we're in, or -1 for `observer`.
 		}
 
 		public class Slot