fix synchronizing plex show metadata (#163)

ErsatzTV.Core/Plex/PlexTelevisionLibraryScanner.cs

@@ -124,8 +124,6 @@ namespace ErsatzTV.Core.Plex
 
             // TODO: this probably doesn't work
             // plex doesn't seem to update genres returned by the main library call
-            if (incomingMetadata.DateUpdated > existingMetadata.DateUpdated)
-            {
             foreach (Genre genre in existingMetadata.Genres
                 .Filter(g => incomingMetadata.Genres.All(g2 => g2.Name != g.Name))
                 .ToList())
@@ -170,6 +168,8 @@ namespace ErsatzTV.Core.Plex
                 }
             }
 
+            if (result.IsUpdated)
+            {
                 await _metadataRepository.MarkAsUpdated(existingMetadata, incomingMetadata.DateUpdated);
             }