fix merge error

Author: thomas694

src/TumblThree/TumblThree.Applications/Crawler/TumblrHiddenCrawler.cs

@@ -476,15 +476,15 @@ private async Task DownloadPage(List<Post> posts)
             }
         }
 
-        private List<Content> GetContents(Post post)
+        private static List<Content> GetContents(Post post)
         {
             if (post.Content?.Count > 0)
             {
                 return post.Content;
             }
             else if (post.Trail?.Count > 0)
             {
-                return post.Trail.Where(.Trail[0].Content;
+                return post.Trail.SelectMany(t => t.Content).ToList();
             }
             return new List<Content>();
         }