fix plex actor artwork for first few actors (#176)

ErsatzTV.Core/Plex/PlexMovieLibraryScanner.cs

@@ -218,7 +218,9 @@ namespace ErsatzTV.Core.Plex
                         }
 
                         foreach (Actor actor in existingMetadata.Actors
-                            .Filter(a => fullMetadata.Actors.All(a2 => a2.Name != a.Name))
+                            .Filter(
+                                a => fullMetadata.Actors.All(
+                                    a2 => a2.Name != a.Name || a.Artwork == null && a2.Artwork != null))
                             .ToList())
                         {
                             existingMetadata.Actors.Remove(actor);

ErsatzTV.Core/Plex/PlexTelevisionLibraryScanner.cs

@@ -181,7 +181,9 @@ namespace ErsatzTV.Core.Plex
                         }
 
                         foreach (Actor actor in existingMetadata.Actors
-                            .Filter(a => fullMetadata.Actors.All(a2 => a2.Name != a.Name))
+                            .Filter(
+                                a => fullMetadata.Actors.All(
+                                    a2 => a2.Name != a.Name || a.Artwork == null && a2.Artwork != null))
                             .ToList())
                         {
                             existingMetadata.Actors.Remove(actor);