Fix the size issue of indicator border in ProgressBar

src/Avalonia.Controls/ProgressBar.cs

@@ -156,6 +156,7 @@ namespace Avalonia.Controls
             MinimumProperty.Changed.AddClassHandler<ProgressBar>((x, e) => x.UpdateIndicatorWhenPropChanged(e));
             MaximumProperty.Changed.AddClassHandler<ProgressBar>((x, e) => x.UpdateIndicatorWhenPropChanged(e));
             IsIndeterminateProperty.Changed.AddClassHandler<ProgressBar>((x, e) => x.UpdateIndicatorWhenPropChanged(e));
+            OrientationProperty.Changed.AddClassHandler<ProgressBar>((x, e) => x.UpdateIndicatorWhenPropChanged(e));
         }
 
         public ProgressBar()
@@ -268,10 +269,18 @@ namespace Avalonia.Controls
                 {
                     double percent = Maximum == Minimum ? 1.0 : (Value - Minimum) / (Maximum - Minimum);
 
+                    // When the Orientation changed, the indicator's Width or Height should set to double.NaN.
                     if (Orientation == Orientation.Horizontal)
+                    {
                         _indicator.Width = barSize.Width * percent;
+                        _indicator.Height = double.NaN;
+                    }
                     else
+                    {
+                        _indicator.Width = double.NaN;
                         _indicator.Height = barSize.Height * percent;
+                    }
+
 
                     Percentage = percent * 100;
                 }