tdf#150916 make unselect in combobox dropdown same as initially unselected

a similar issue as seen in tdf#148197

Change-Id: I3848fe7b48f6148a5ae13d484c866953fed83c90
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/140605
Tested-by: Jenkins
Reviewed-by: Adolfo Jayme Barrientos <fitojb@ubuntu.com>
diff --git a/vcl/unx/gtk3/gtkinst.cxx b/vcl/unx/gtk3/gtkinst.cxx
index ca36152..690f39a 100644
--- a/vcl/unx/gtk3/gtkinst.cxx
+++ b/vcl/unx/gtk3/gtkinst.cxx
@@ -20820,22 +20820,24 @@ private:

    void tree_view_set_cursor(int pos)
    {
        GtkTreePath* path;
        if (pos == -1)
        {
            path = gtk_tree_path_new();
            gtk_tree_selection_unselect_all(gtk_tree_view_get_selection(m_pTreeView));
            if (m_pCellView)
                gtk_cell_view_set_displayed_row(m_pCellView, nullptr);
        }
        else
        {
            GtkTreePath* path = gtk_tree_path_new_from_indices(pos, -1);
            path = gtk_tree_path_new_from_indices(pos, -1);
            if (gtk_tree_view_get_model(m_pTreeView))
                gtk_tree_view_scroll_to_cell(m_pTreeView, path, nullptr, false, 0, 0);
            gtk_tree_view_set_cursor(m_pTreeView, path, nullptr, false);
            if (m_pCellView)
                gtk_cell_view_set_displayed_row(m_pCellView, path);
            gtk_tree_path_free(path);
        }
        gtk_tree_view_set_cursor(m_pTreeView, path, nullptr, false);
        gtk_tree_path_free(path);
    }

    int tree_view_get_cursor() const