Fix bug in file manager

Author: rxtur

src/Core/Constants.cs

@@ -4,5 +4,6 @@ public class Constants
     {
         public static string NewestVersion = "last-version";
         public static string UpgradeDirectory = "_upgrade";
+        public static string DefaultAvatar = "lib/img/avatar.png";
     }
 }

src/Core/Data/Repositories/AuthorRepository.cs

@@ -63,6 +63,7 @@ public async Task Save(Author author)
             if (author.Created == DateTime.MinValue)
             {
                 author.DisplayName = author.AppUserName;
+                author.Avatar = Constants.DefaultAvatar;
                 author.Created = SystemClock.Now();
                 await _db.Authors.AddAsync(author);
             }

src/Core/Services/StorageService.cs

@@ -410,19 +410,22 @@ List<AssetItem> MapFilesToAssets(IList<string> assets)
         {
             var items = new List<AssetItem>();
 
-            foreach (var asset in assets)
+            if (assets != null && assets.Any())
             {
-                // Azure puts web sites under "wwwroot" folder
-                var path = asset.Replace($"wwwroot{_separator}wwwroot", "wwwroot", StringComparison.OrdinalIgnoreCase);
-
-                items.Add(new AssetItem {
-                    Path = asset,
-                    Url = pathToUrl(path),
-                    Title = pathToTitle(path),
-                    Image = pathToImage(path)
-                });
-            }
+                foreach (var asset in assets)
+                {
+                    // Azure puts web sites under "wwwroot" folder
+                    var path = asset.Replace($"wwwroot{_separator}wwwroot", "wwwroot", StringComparison.OrdinalIgnoreCase);
 
+                    items.Add(new AssetItem
+                    {
+                        Path = asset,
+                        Url = pathToUrl(path),
+                        Title = pathToTitle(path),
+                        Image = pathToImage(path)
+                    });
+                }
+            }
             return items;
         }