Display default avatar for avatars from enterprise hosts.

Fixes #1870.

Author: grokys

src/GitHub.App/ViewModels/ActorViewModel.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Windows.Media.Imaging;
 using GitHub.Models;
+using GitHub.Primitives;
 using GitHub.Services;
 
 namespace GitHub.ViewModels
@@ -16,10 +17,30 @@ public ActorViewModel()
         public ActorViewModel(ActorModel model)
         {
             Login = model?.Login ?? "[unknown]";
-            Avatar = model?.AvatarUrl != null ?
-                new BitmapImage(new Uri(model.AvatarUrl)) :
-                AvatarProvider.CreateBitmapImage(DefaultAvatar);
-            AvatarUrl = model?.AvatarUrl ?? DefaultAvatar;
+
+            if (model?.AvatarUrl != null)
+            {
+                try
+                {
+                    var uri = new Uri(model.AvatarUrl);
+
+                    // Image requests to enterprise hosts over https always fail currently,
+                    // so just display the default avatar. See #1547.
+                    if (uri.Scheme != "https" ||
+                        uri.Host.EndsWith("githubusercontent.com", StringComparison.OrdinalIgnoreCase))
+                    {
+                        AvatarUrl = model.AvatarUrl;
+                        Avatar = new BitmapImage(new Uri(AvatarUrl));
+                    }
+                }
+                catch { }
+            }
+
+            if (AvatarUrl == null)
+            {
+                Avatar = AvatarProvider.CreateBitmapImage(DefaultAvatar);
+                AvatarUrl = DefaultAvatar;
+            }
         }
 
         public BitmapSource Avatar { get; set; }