fix focusing bug in SharpTreeView

src/Libraries/SharpTreeView/ICSharpCode.TreeView/SharpTreeView.cs

@@ -151,7 +151,7 @@ namespace ICSharpCode.TreeView
 				if (selectedOldItems != null) {
 					var list = SelectedItems.Cast<SharpTreeNode>().Except(selectedOldItems).ToList();
 					SetSelectedItems(list);
-					if (SelectedItem == null) {
+					if (SelectedItem == null && this.IsKeyboardFocusWithin) {
 						// if we removed all selected nodes, then move the focus to the node 
 						// preceding the first of the old selected nodes
 						SelectedIndex = Math.Max(0, e.OldStartingIndex - 1);