Fix 8 design majors: optional ILogger in libraries, IndexFactoryService singleton threading, SharedMediaTypeRegistry, required TrackDto fields, GetExtensionType dedup, PagedResult zero-guard, TrackService null-return on failure

DeepDrftModels/Models/PagedResult.cs

@@ -6,7 +6,7 @@ public class PagedResult<T>
     public int TotalCount { get; set; }
     public int Page { get; set; }
     public int PageSize { get; set; }
-    public int TotalPages => (int)Math.Ceiling((double)TotalCount / PageSize);
+    public int TotalPages => PageSize > 0 ? (int)Math.Ceiling((double)TotalCount / PageSize) : 0;
     public bool HasNextPage => Page < TotalPages;
     public bool HasPreviousPage => Page > 1;
 
@@ -27,7 +27,7 @@ public class PagedResult<T>
 
     public PagedResult(IEnumerable<T> items, int totalCount, int page, int pageSize)
     {
-        Items = items.ToList() ?? new List<T>();
+        Items = items.ToList();
         TotalCount = totalCount;
         Page = page;
         PageSize = pageSize;