fix: close #1305.

src/Shared/HandyControl_Shared/Tools/Converter/DataGridSelectAllButtonVisibilityConverter.cs

@@ -10,43 +10,11 @@ public class DataGridSelectAllButtonVisibilityConverter : IMultiValueConverter
 {
     public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
     {
-        if (values == null)
+        if (values?.Length is 2 &&
+            values[0] is DataGridHeadersVisibility.All &&
+            values[1] is bool showButton)
         {
-            return Visibility.Collapsed;
-        }
-
-        if (values.Length != 2)
-        {
-            return Visibility.Collapsed;
-        }
-
-        if (values[0] is DataGridHeadersVisibility headersVisibility)
-        {
-            if (values[1] is bool showButton)
-            {
-                if (headersVisibility == DataGridHeadersVisibility.All)
-                {
-                    return showButton ? Visibility.Visible : Visibility.Collapsed;
-                }
-
-                return Visibility.Collapsed;
-            }
-
-            return Visibility.Collapsed;
-        }
-        else if (values[0] is bool showButton)
-        {
-            if (values[1] is DataGridHeadersVisibility visibility)
-            {
-                if (visibility == DataGridHeadersVisibility.All)
-                {
-                    return showButton ? Visibility.Visible : Visibility.Collapsed;
-                }
-
-                return Visibility.Collapsed;
-            }
-
-            return Visibility.Collapsed;
+            return showButton ? Visibility.Visible : Visibility.Hidden;
         }
 
         return Visibility.Collapsed;