Fix existing media segments not being handled on scan (#14218)

MediaBrowser.Model/MediaSegments/MediaSegmentGenerationRequest.cs

@@ -1,4 +1,7 @@
 using System;
+using System.Collections.Generic;
+using Jellyfin.Database.Implementations.Entities;
+using MediaBrowser.Model.MediaSegments;
 
 namespace MediaBrowser.Model;
 
@@ -11,4 +14,9 @@ public record MediaSegmentGenerationRequest
     /// Gets the Id to the BaseItem the segments should be extracted from.
     /// </summary>
     public Guid ItemId { get; init; }
+
+    /// <summary>
+    /// Gets existing media segments generated on an earlier scan by this provider.
+    /// </summary>
+    public required IReadOnlyList<MediaSegmentDto> ExistingSegments { get; init; }
 }