cannot click on expand/collapse icon if left edge of row is beyond first column

If you call setFirstColumnSpanned() on a row, but the left edge of the row is to the right of the first column, you cannot click on the row's expand/collapse icon. QTreeViewPrivate::itemDecorationAt() returns -1 in that case, because QHeaderView::logicalIndexAt() returns a non-zero column. It seems to me that itemDecorationAt() should take spanning into account.