fix changing default alternate schedule (#2331)

CHANGELOG.md

@@ -75,6 +75,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - Fix incorrect media item counts after removing paths from local libraries
 - Fix song playback in playback troubleshooting
 - Fix seeking into extracted text subtitles
+- Fix error when changing default (lowest priority) alternate schedule
 
 ### Changed
 - Allow multiple watermarks in playback troubleshooting

ErsatzTV.Application/Playouts/Commands/ReplacePlayoutAlternateScheduleItemsHandler.cs

@@ -112,13 +112,19 @@ public class ReplacePlayoutAlternateScheduleItemsHandler :
                 }
 
                 // save highest index directly to playout
-                if (playout.ProgramScheduleId != highest.ProgramScheduleId)
+                bool hasDefaultScheduleChange = playout.ProgramScheduleId != highest.ProgramScheduleId;
+                if (hasDefaultScheduleChange)
                 {
                     playout.ProgramScheduleId = highest.ProgramScheduleId;
                 }
 
                 await dbContext.SaveChangesAsync(cancellationToken);
 
+                if (hasDefaultScheduleChange)
+                {
+                    await dbContext.Entry(playout).Reference(p => p.ProgramSchedule).LoadAsync(cancellationToken);
+                }
+
                 // load newly-added schedules
                 foreach (ProgramScheduleAlternate alternate in playout.ProgramScheduleAlternates
                              .Where(alternate => alternate.ProgramSchedule is null))