Merge pull request #4698 from AvaloniaUI/fixes/small-selection-fixes

Some small selection fixes

src/Avalonia.Controls/Primitives/SelectingItemsControl.cs

@@ -491,8 +491,7 @@ namespace Avalonia.Controls.Primitives
 
                 if (ItemCount > 0 &&
                     Match(keymap.SelectAll) &&
-                    (((SelectionMode & SelectionMode.Multiple) != 0) ||
-                      (SelectionMode & SelectionMode.Toggle) != 0))
+                    SelectionMode.HasFlag(SelectionMode.Multiple))
                 {
                     Selection.SelectAll();
                     e.Handled = true;

src/Avalonia.Controls/Selection/InternalSelectionModel.cs

@@ -63,6 +63,11 @@ namespace Avalonia.Controls.Selection
 
         private protected override void SetSource(IEnumerable? value)
         {
+            if (Source == value)
+            {
+                return;
+            }
+
             object?[]? oldSelection = null;
 
             if (Source is object && value is object)

src/Avalonia.Layout/FlowLayoutAlgorithm.cs

@@ -211,7 +211,7 @@ namespace Avalonia.Layout
                             anchorPosition = new Point(anchorBounds.X, anchorBounds.Y);
                         }
                     }
-                    else
+                    else if (anchorIndex >= 0)
                     {
                         // It is possible to end up in a situation during a collection change where GetAnchorForTargetElement returns an index
                         // which is not in the realized range. Eg. insert one item at index 0 for a grid layout.