Fix attempt to change ruleset/beatmap bindables while screen is not active

osu.Game/Screens/Play/Spectator.cs

@@ -63,6 +63,11 @@ public class Spectator : OsuScreen
 
         private IBindable<WeakReference<BeatmapSetInfo>> managerUpdated;
 
+        /// <summary>
+        /// Becomes true if a new state is waiting to be loaded (while this screen was not active).
+        /// </summary>
+        private bool newStatePending;
+
         public Spectator([NotNull] User targetUser)
         {
             this.targetUser = targetUser ?? throw new ArgumentNullException(nameof(targetUser));
@@ -162,7 +167,21 @@ private void userBeganPlaying(int userId, SpectatorState state)
 
             this.state = state;
 
-            Schedule(attemptStart);
+            if (this.IsCurrentScreen())
+                Schedule(attemptStart);
+            else
+                newStatePending = true;
+        }
+
+        public override void OnResuming(IScreen last)
+        {
+            base.OnResuming(last);
+
+            if (newStatePending)
+            {
+                attemptStart();
+                newStatePending = false;
+            }
         }
 
         private void userFinishedPlaying(int userId, SpectatorState state)