Fix background beatmap processor thread not correctly exiting

osu.Game/BackgroundBeatmapProcessor.cs

@@ -189,6 +189,10 @@ private void processScoresWithMissingStatistics()
 
                     Logger.Log($"Populated maximum statistics for score {id}");
                 }
+                catch (ObjectDisposedException)
+                {
+                    throw;
+                }
                 catch (Exception e)
                 {
                     Logger.Log(@$"Failed to populate maximum statistics for {id}: {e}");
@@ -237,6 +241,10 @@ private void convertLegacyTotalScoreToStandardised()
                     Logger.Log($"Converted total score for score {id}");
                     ++processedCount;
                 }
+                catch (ObjectDisposedException)
+                {
+                    throw;
+                }
                 catch (Exception e)
                 {
                     Logger.Log($"Failed to convert total score for {id}: {e}");