Refactor column layout calculation to improve handling of star width constraints

Author: JakkuSakura

src/Avalonia.Controls.TreeDataGrid/Models/TreeDataGrid/ColumnList.cs

@@ -160,22 +160,28 @@ private void UpdateColumnSizes()
                 // the star width for the non-constrained columns.
                 if (starWidthWasConstrained && MathUtilities.GreaterThan(availableSpace, 0))
                 {
+                    var remainingSpace = availableSpace;
+                    var remainingStars = totalStars;
+
                     for (var i = 0; i < Count; ++i)
                     {
                         var column = (IUpdateColumnLayout)this[i];
 
                         if (column.StarWidthWasConstrained)
                         {
-                            availableSpace -= column.ActualWidth;
-                            totalStars -= column.Width.Value;
+                            remainingSpace -= column.ActualWidth;
+                            remainingStars -= column.Width.Value;
                         }
                     }
 
-                    for (var i = 0; i < Count; ++i)
+                    if (remainingStars > 0)
                     {
-                        var column = (IUpdateColumnLayout)this[i];
-                        if (column.Width.IsStar && !column.StarWidthWasConstrained)
-                            column.CalculateStarWidth(availableSpace, totalStars);
+                        for (var i = 0; i < Count; ++i)
+                        {
+                            var column = (IUpdateColumnLayout)this[i];
+                            if (column.Width.IsStar && !column.StarWidthWasConstrained)
+                                column.CalculateStarWidth(remainingSpace, remainingStars);
+                        }
                     }
                 }