/* cannot continue if no stop position set or invalid offset */
g_return_val_if_fail (stop != -1, 0);
g_return_val_if_fail (stop >= offset, 0);
/* cannot continue if no stop position set or invalid offset */
g_return_val_if_fail (stop != -1, 0);
g_return_val_if_fail (stop >= offset, 0);