Set placeholder only if something goes wrong (IOS-238)

MastodonSDK/Sources/MastodonUI/Extension/FLAnimatedImageView.swift

@@ -45,11 +45,14 @@ extension FLAnimatedImageView {
         // cancel task
         cancelTask()
         
-        // set placeholder
-        image = placeholder
-        
         // set image
-        guard let url = url else { return }
+        guard let url else {
+            DispatchQueue.main.async { [weak self] in
+                self?.image = placeholder
+            }
+            return
+        }
+
         activeAvatarRequestURL = url
         let avatarRequest = AF.request(url).publishData()
         avatarRequestCancellable = avatarRequest
@@ -78,7 +81,9 @@ extension FLAnimatedImageView {
                         }
                     }
                 case .failure:
-                    break
+                    DispatchQueue.main.async { [weak self] in
+                        self?.image = placeholder
+                    }
                 }
             }
     }