fix adding items to empty playlists (#1784)

CHANGELOG.md

@@ -14,6 +14,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - Add basic cache busting to XMLTV image URLs
   - This should help with clients not showing correct channel logos or posters
 - Fix artwork in other video libraries by @raknam
+- Fix adding items to empty playlists
 
 ### Changed
 - Remove some unnecessary API calls related to media server scanning and paging

ErsatzTV.Application/MediaCollections/Commands/AddItemsToPlaylistHandler.cs

@@ -48,7 +48,7 @@ public class AddItemsToPlaylistHandler : IRequestHandler<AddItemsToPlaylist, Eit
             { ProgramScheduleItemCollectionType.Image, request.ImageIds }
         };
 
-        int index = playlist.Items.Max(i => i.Index) + 1;
+        int index = playlist.Items.Count > 0 ? playlist.Items.Max(i => i.Index) + 1 : 0;
 
         foreach ((ProgramScheduleItemCollectionType collectionType, List<int> ids) in allItems)
         {