UI - Use Timer instead of DispatcherTimer where feasible

src/Artemis.UI.Shared/Controls/DeviceVisualizer.cs

@@ -34,7 +34,7 @@ public class DeviceVisualizer : Control
     /// <inheritdoc />
     public DeviceVisualizer()
     {
-        _timer = new DispatcherTimer(DispatcherPriority.Render) {Interval = TimeSpan.FromMilliseconds(1000.0 / UpdateFrameRate)};
+        _timer = new DispatcherTimer(DispatcherPriority.Background) {Interval = TimeSpan.FromMilliseconds(1000.0 / UpdateFrameRate)};
         _deviceVisualizerLeds = new List<DeviceVisualizerLed>();
 
         PointerReleased += OnPointerReleased;

src/Artemis.UI.Shared/Services/Builders/OpenFileDialogBuilder.cs

@@ -78,6 +78,6 @@ public class OpenFileDialogBuilder
     public async Task<string[]?> ShowAsync()
     {
         IReadOnlyList<IStorageFile> files = await _parent.StorageProvider.OpenFilePickerAsync(_options);
-        return files.Select(f => f.Path.LocalPath).ToArray();
+        return files.Count == 0 ? null : files.Select(f => f.Path.LocalPath).ToArray();
     }
 }