Gravar-mail: Poly[[[μ(3)-(E)-N-(pyridin-4-yl­methyl­idene)hy­droxy­laminato-κ(3) O:N:N′][μ(2)-(E)-N-(pyridin-4-yl­methyl­idene)hydroxyl­amine-κ(2) N:N′][(E)-N-(pyridin-4-yl­methyl­idene-κN)hydroxyl­amine]­disilver(I)] nitrate]