Council Regulation (EC) No 1623/2003 of 11 September 2003 extending the definitive anti-dumping duty imposed by Regulation (EC) No 408/2002 on imports of certain zinc oxides originating in the People's Republic of China to imports of certain zinc oxides consigned from Vietnam, whether declared as originating in Vietnam or not, and to imports of certain zinc oxides originating in the People's Republic of China and mixed with silica