fix(donut): allow returning to a disabled front face

src/Filee.App/ViewModels/RadialViewModel.cs

@@ -228,7 +228,8 @@ private void ShowFace(bool back, bool checkBack = true)
             Items = face.Items;
         }
         var other = back ? _front : checkBack ? BackFace() : _back;
-        CanFlip = other?.IsUsable == true;
+        // The front was already shown, even when every slice was disabled. Do not strand the user on the back face.
+        CanFlip = back ? _front.Items.Count > 0 : other?.IsUsable == true;
         var how = FlipKey is { } key ? KeyNames.Display(key) : "";
         FlipHint = CanFlip && (FlipKey is not null || FlipWithWheel)
             ? loc.Format(back ? "donut.flip_to_front" : "donut.flip_to_back", how).Trim()

tests/Filee.App.Tests/DonutFlipTests.cs

@@ -735,6 +735,24 @@ public void A_donut_without_a_back_face_does_not_flip() => With(animations: true
         window.Close();
     });
 
+    [AvaloniaFact]
+    public void A_disabled_front_face_is_still_reachable_after_flipping_to_a_usable_back() =>
+        With(animations: false, back: ["to-gif"], () =>
+        {
+            Images.PresetIds = ["to-wav"];
+            var (vm, window, donut) = OpenClickMode();
+            try
+            {
+                Assert.All(vm.Items, item => Assert.False(item.IsEnabled));
+                Assert.True(donut.Flip());
+                Assert.True(vm.IsBackFace);
+                Assert.True(vm.CanFlip);
+                Assert.True(donut.Flip());
+                Assert.False(vm.IsBackFace);
+            }
+            finally { window.Close(); }
+        });
+
     [AvaloniaFact]
     public void The_back_face_greys_out_what_cannot_convert_the_files_and_one_with_nothing_left_does_not_flip()
     {