Move finaliser inside disposal region

osu.Game/Beatmaps/WorkingBeatmap.cs

@@ -46,11 +46,6 @@ namespace osu.Game.Beatmaps
             skin = new RecyclableLazy<Skin>(GetSkin);
         }
 
-        ~WorkingBeatmap()
-        {
-            Dispose(false);
-        }
-
         protected virtual Track GetVirtualTrack()
         {
             const double excess_length = 1000;
@@ -229,6 +224,11 @@ namespace osu.Game.Beatmaps
             beatmapCancellation.Cancel();
         }
 
+        ~WorkingBeatmap()
+        {
+            Dispose(false);
+        }
+
         #endregion
 
         public class RecyclableLazy<T>