Prevent saving and starting a map when max player count is exceeded.

OpenRA.Game/Map/Map.cs

@@ -336,9 +336,6 @@ namespace OpenRA
 				throw new InvalidDataException($"Map format {MapFormat} is not supported.\n File: {package.Name}");
 
 			PlayerDefinitions = MiniYaml.NodesOrEmpty(yaml, "Players");
-			if (PlayerDefinitions.Count > 64)
-				throw new InvalidDataException($"Maps must not define more than 64 players.\n File: {package.Name}");
-
 			ActorDefinitions = MiniYaml.NodesOrEmpty(yaml, "Actors");
 
 			Grid = modData.Manifest.Get<MapGrid>();

OpenRA.Game/Map/MapPlayers.cs

@@ -17,6 +17,10 @@ namespace OpenRA
 {
 	public class MapPlayers
 	{
+		// Player masks are represented using a 64 bit integer
+		// The "Everyone" player for spectators is created at runtime,
+		// reducing the available player count for maps by 1.
+		public const int MaximumPlayerCount = 63;
 		public readonly Dictionary<string, PlayerReference> Players;
 
 		public MapPlayers()