Clean up abandoned games on disconnect

When a client disconnects without ever having joined a game, it leaves
behind an empty game on the server. Remove these when a player
disconnects.

Co-Authored-By: js6pak <me@6pak.dev>

src/Impostor.Server/Net/Client.cs

@@ -373,6 +373,7 @@ namespace Impostor.Server.Net
 
             _logger.LogInformation("Client {0} disconnecting, reason: {1}", Id, reason);
             _clientManager.Remove(this);
+            await _gameManager.OnClientDisconnectAsync(this);
         }
 
         private bool IsPacketAllowed(IMessageReader message, bool hostOnly)

src/Impostor.Server/Net/Manager/GameManager.cs

@@ -142,5 +142,14 @@ namespace Impostor.Server.Net.Manager
 
             return (true, game);
         }
+
+        internal async ValueTask OnClientDisconnectAsync(IClient client)
+        {
+            if (_gamesCreatedBy.TryRemove(client, out var game) && game is { PlayerCount: 0, GameState: not GameStates.Destroyed })
+            {
+                _logger.LogWarning("Client {Name}({ClientId}) left empty game open when disconnecting", client.Name, client.Id);
+                await RemoveAsync(game.Code);
+            }
+        }
     }
 }