attribute: also put selected item on top if sorting descending (fixes #12434)

(cherry picked from commit d3c4da0)

Author: jef-n

src/gui/attributetable/qgsattributetablefiltermodel.cpp

@@ -48,11 +48,11 @@ bool QgsAttributeTableFilterModel::lessThan( const QModelIndex &left, const QMod
 
     if ( leftSelected && !rightSelected )
     {
-      return true;
+      return sortOrder() == Qt::AscendingOrder;
     }
     else if ( rightSelected && !leftSelected )
     {
-      return false;
+      return sortOrder() == Qt::DescendingOrder;
     }
   }