Cancel ApplyDefaults() when requested

Also didn't notice a particular case here, but if all code passes up
until we get to the `foreach (var h in nestedHitObjects)` below, then we
could end up stuck here for quite a while.

osu.Game/Rulesets/Objects/HitObject.cs

@@ -104,6 +104,8 @@ namespace osu.Game.Rulesets.Objects
         /// <param name="cancellationToken">The cancellation token.</param>
         public void ApplyDefaults(ControlPointInfo controlPointInfo, IBeatmapDifficultyInfo difficulty, CancellationToken cancellationToken = default)
         {
+            cancellationToken.ThrowIfCancellationRequested();
+
             ApplyDefaultsToSelf(controlPointInfo, difficulty);
 
             nestedHitObjects.Clear();