Revert "remove redundant line causing NullReferenceException when slu…

…g is empty (madskristensen#52)"

This reverts commit a9f62a4.

src/Controllers/BlogController.cs

@@ -205,6 +205,7 @@ public async Task<IActionResult> UpdatePost(Post post)
                 .ToList()
                 .ForEach(existing.Categories.Add);
             existing.Title = post.Title.Trim();
+            existing.Slug = post.Slug.Trim();
             existing.Slug = !string.IsNullOrWhiteSpace(post.Slug) ? post.Slug.Trim() : Models.Post.CreateSlug(post.Title);
             existing.IsPublished = post.IsPublished;
             existing.Content = post.Content.Trim();