Gravar-mail: catena-Poly[[(2-amino-1,3-benzothia­zole-6-carboxyl­ato-κ(2) O,O′)(2,2′-bipyridyl-κ(2) N,N′)cadmium]-μ-2-amino-1,3-benzothia­zole-6-carboxyl­ato-κ(3) N (1):O,O′]