Fix lobby exception (#4544)

From what I could tell whenever LobbyState is entered it makes a new Lobby + CharacterSetup GUI via Startup. These events are never disposed of under Shutdown + the lobby should be null whenever we're not in LobbyState (as the control ends up disposed).

The lobby == null checks could probably also be null asserts as they shouldn't be null when those methods are being called.

Content.Client/Lobby/LobbyState.cs

@@ -8,11 +8,8 @@ using Content.Client.LateJoin;
 using Content.Client.Lobby.UI;
 using Content.Client.Preferences;
 using Content.Client.Preferences.UI;
-using Content.Client.Viewport;
 using Content.Client.Voting;
-using Content.Shared.Chat;
 using Content.Shared.GameTicking;
-using Content.Shared.Input;
 using Robust.Client;
 using Robust.Client.Console;
 using Robust.Client.Input;
@@ -21,7 +18,6 @@ using Robust.Client.ResourceManagement;
 using Robust.Client.UserInterface;
 using Robust.Client.UserInterface.Controls;
 using Robust.Shared.GameObjects;
-using Robust.Shared.Input.Binding;
 using Robust.Shared.IoC;
 using Robust.Shared.Localization;
 using Robust.Shared.Prototypes;
@@ -45,8 +41,8 @@ namespace Content.Client.Lobby
         [Dependency] private readonly IGameTiming _gameTiming = default!;
         [Dependency] private readonly IVoteManager _voteManager = default!;
 
-        [ViewVariables] private CharacterSetupGui _characterSetup = default!;
+        [ViewVariables] private CharacterSetupGui? _characterSetup;
-        [ViewVariables] private LobbyGui _lobby = default!;
+        [ViewVariables] private LobbyGui? _lobby;
 
         public override void Startup()
         {
@@ -55,6 +51,9 @@ namespace Content.Client.Lobby
                 _prototypeManager);
             LayoutContainer.SetAnchorPreset(_characterSetup, LayoutContainer.LayoutPreset.Wide);
 
+            _lobby = new LobbyGui(_entityManager, _preferencesManager);
+            _userInterfaceManager.StateRoot.AddChild(_lobby);
+
             _characterSetup.CloseButton.OnPressed += _ =>
             {
                 _userInterfaceManager.StateRoot.AddChild(_lobby);
@@ -67,9 +66,6 @@ namespace Content.Client.Lobby
                 _lobby?.CharacterPreview.UpdateUI();
             };
 
-            _lobby = new LobbyGui(_entityManager, _preferencesManager);
-            _userInterfaceManager.StateRoot.AddChild(_lobby);
-
             LayoutContainer.SetAnchorPreset(_lobby, LayoutContainer.LayoutPreset.Wide);
 
             _chatManager.SetChatBox(_lobby.Chat);
@@ -119,12 +115,22 @@ namespace Content.Client.Lobby
         public override void Shutdown()
         {
             _playerManager.PlayerListUpdated -= PlayerManagerOnPlayerListUpdated;
-            _lobby.Dispose();
+            var gameTicker = EntitySystem.Get<ClientGameTicker>();
-            _characterSetup.Dispose();
+            gameTicker.InfoBlobUpdated -= UpdateLobbyUi;
+            gameTicker.LobbyStatusUpdated -= LobbyStatusUpdated;
+            gameTicker.LobbyReadyUpdated -= LobbyReadyUpdated;
+            gameTicker.LobbyLateJoinStatusUpdated -= LobbyLateJoinStatusUpdated;
+
+            _lobby?.Dispose();
+            _characterSetup?.Dispose();
+            _lobby = null;
+            _characterSetup = null;
         }
 
         public override void FrameUpdate(FrameEventArgs e)
         {
+            if (_lobby == null) return;
+
             var gameTicker = EntitySystem.Get<ClientGameTicker>();
             if (gameTicker.IsGameStarted)
             {
@@ -183,15 +189,13 @@ namespace Content.Client.Lobby
 
         private void LobbyLateJoinStatusUpdated()
         {
+            if (_lobby == null) return;
             _lobby.ReadyButton.Disabled = EntitySystem.Get<ClientGameTicker>().DisallowedLateJoin;
         }
 
         private void UpdateLobbyUi()
         {
-            if (_lobby == null)
+            if (_lobby == null) return;
-            {
-                return;
-            }
 
             var gameTicker = EntitySystem.Get<ClientGameTicker>();
 
@@ -218,6 +222,7 @@ namespace Content.Client.Lobby
 
         private void UpdatePlayerList()
         {
+            if (_lobby == null) return;
             _lobby.OnlinePlayerList.Clear();
             var gameTicker = EntitySystem.Get<ClientGameTicker>();