fix: fixed UniformSpacingPanel measure issue

src/Shared/HandyControl_Shared/Controls/Panel/UniformSpacingPanel.cs

@@ -1,5 +1,6 @@
 using System;
 using System.ComponentModel;
+using System.Diagnostics;
 using System.Windows;
 using System.Windows.Controls;
 using HandyControl.Data;
@@ -237,8 +238,6 @@ public class UniformSpacingPanel : Panel
                         panelSize.V += sz.V + spacingSize.V;
                         curLineSize = new PanelUvSize(_orientation);
                     }
-
-                    isFirst = true;
                 }
                 else
                 {
@@ -379,6 +378,7 @@ public class UniformSpacingPanel : Panel
             ArrangeLine(uvFinalSize.V, useItemU, itemU, spacingSize.U);
         }
 
+        Trace.WriteLine(finalSize.Width);
         return finalSize;
     }
 }