Fix deadlock when logging out while at the create match screen

Closes https://github.com/ppy/osu/issues/24275.

osu.Game/Screens/OnlinePlay/Match/RoomSubScreen.cs

@@ -23,6 +23,7 @@ using osu.Framework.Screens;
 using osu.Game.Audio;
 using osu.Game.Beatmaps;
 using osu.Game.Input.Bindings;
+using osu.Game.Online.API;
 using osu.Game.Online.Rooms;
 using osu.Game.Overlays;
 using osu.Game.Overlays.Mods;
@@ -76,6 +77,9 @@ namespace osu.Game.Screens.OnlinePlay.Match
         [Resolved]
         private RulesetStore rulesets { get; set; }
 
+        [Resolved]
+        private IAPIProvider api { get; set; } = null!;
+
         [Resolved(canBeNull: true)]
         protected OnlinePlayScreen ParentScreen { get; private set; }
 
@@ -284,6 +288,8 @@ namespace osu.Game.Screens.OnlinePlay.Match
         [Resolved(canBeNull: true)]
         private IDialogOverlay dialogOverlay { get; set; }
 
+        protected virtual bool IsConnected => api.State.Value == APIState.Online;
+
         public override bool OnBackButton()
         {
             if (Room.RoomID.Value == null)
@@ -356,6 +362,9 @@ namespace osu.Game.Screens.OnlinePlay.Match
             if (ExitConfirmed)
                 return true;
 
+            if (!IsConnected)
+                return true;
+
             if (dialogOverlay == null || Room.RoomID.Value != null || Room.Playlist.Count == 0)
                 return true;
 

osu.Game/Screens/OnlinePlay/Multiplayer/MultiplayerMatchSubScreen.cs

@@ -17,7 +17,6 @@ using osu.Game.Beatmaps;
 using osu.Game.Configuration;
 using osu.Game.Graphics.Cursor;
 using osu.Game.Online;
-using osu.Game.Online.API;
 using osu.Game.Online.Multiplayer;
 using osu.Game.Online.Rooms;
 using osu.Game.Overlays;
@@ -50,9 +49,6 @@ namespace osu.Game.Screens.OnlinePlay.Multiplayer
         [Resolved]
         private MultiplayerClient client { get; set; }
 
-        [Resolved]
-        private IAPIProvider api { get; set; }
-
         [Resolved(canBeNull: true)]
         private OsuGame game { get; set; }
 
@@ -79,6 +75,8 @@ namespace osu.Game.Screens.OnlinePlay.Multiplayer
                 handleRoomLost();
         }
 
+        protected override bool IsConnected => base.IsConnected && client.IsConnected.Value;
+
         protected override Drawable CreateMainContent() => new Container
         {
             RelativeSizeAxes = Axes.Both,
@@ -253,14 +251,10 @@ namespace osu.Game.Screens.OnlinePlay.Multiplayer
         private bool exitConfirmed;
 
         public override bool OnExiting(ScreenExitEvent e)
-        {
-            // the room may not be left immediately after a disconnection due to async flow,
-            // so checking the MultiplayerClient / IAPIAccess statuses is also required.
-            if (client.Room == null || !client.IsConnected.Value || api.State.Value != APIState.Online)
         {
             // room has not been created yet or we're offline; exit immediately.
+            if (client.Room == null || !IsConnected)
                 return base.OnExiting(e);
-            }
 
             if (!exitConfirmed && dialogOverlay != null)
             {

osu.Game/Screens/OnlinePlay/OnlinePlaySubScreen.cs

@@ -1,8 +1,6 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
-#nullable disable
-
 using osu.Framework.Allocation;
 using osu.Framework.Graphics;
 using osu.Framework.Screens;
@@ -15,8 +13,8 @@ namespace osu.Game.Screens.OnlinePlay
 
         public virtual string ShortTitle => Title;
 
-        [Resolved(CanBeNull = true)]
+        [Resolved]
-        protected IRoomManager RoomManager { get; private set; }
+        protected IRoomManager? RoomManager { get; private set; }
 
         protected OnlinePlaySubScreen()
         {