SongSelectV2: Fix more crashes resulting from users deliberately trying to break things

See https://github.com/ppy/osu/issues/33336#issuecomment-2922443444.

Can't wait for even more human fuzzing to come later.

osu.Game/Screens/SelectV2/SoloSongSelect.cs

@@ -143,6 +143,9 @@ namespace osu.Game.Screens.SelectV2
 
         private void edit(BeatmapInfo beatmap)
         {
+            if (!this.IsCurrentScreen())
+                return;
+
             FinaliseSelection();
 
             // Forced refetch is important here to guarantee correct invalidation across all difficulties.

osu.Game/Screens/SelectV2/SongSelect.cs

@@ -390,6 +390,9 @@ namespace osu.Game.Screens.SelectV2
 
         private void selectBeatmap(BeatmapInfo beatmap)
         {
+            if (!this.IsCurrentScreen())
+                return;
+
             if (beatmap.BeatmapSet!.Protected)
                 return;
 
@@ -674,6 +677,9 @@ namespace osu.Game.Screens.SelectV2
         /// </summary>
         public void SelectAndStart(BeatmapInfo beatmap)
         {
+            if (!this.IsCurrentScreen())
+                return;
+
             Beatmap.Value = beatmaps.GetWorkingBeatmap(beatmap);
             OnStart();
         }