Fix onLoadRequested getting early-exited too early in spectator scenarios

In some scenarios, multiplayer spectator would not tick over to the next
beatmap.

Here's an example:

- Room has two items queued
- Local user starts download of both
- First beatmap starts and download is complete
- First beatmap ends (spectating is active)
- Second beatmap starts but download is not complete

In this scenario, the local client will get stuck at the spectator
screen due to the `onLoadRequested`-invoked screen change being early
exited.

It would require manual recovery (clicking back button) to return to a
sane state.

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

@@ -371,9 +371,6 @@ namespace osu.Game.Screens.OnlinePlay.Multiplayer
 
         private void onLoadRequested()
         {
-            if (BeatmapAvailability.Value.State != DownloadState.LocallyAvailable)
-                return;
-
             // In the case of spectating, IMultiplayerClient.LoadRequested can be fired while the game is still spectating a previous session.
             // For now, we want to game to switch to the new game so need to request exiting from the play screen.
             if (!ParentScreen.IsCurrentScreen())
@@ -391,6 +388,9 @@ namespace osu.Game.Screens.OnlinePlay.Multiplayer
             if (client.LocalUser?.State == MultiplayerUserState.Spectating && (SelectedItem.Value == null || Beatmap.IsDefault))
                 return;
 
+            if (BeatmapAvailability.Value.State != DownloadState.LocallyAvailable)
+                return;
+
             StartPlay();
         }