I'm reading Harry Potter in Japanese and it goes:

力は失せ、命も絶えなんとする姿で、ヴォルデモートは逃げ去った。
His powers gone, his life almost extinguished, Voldemort had fled;

命も絶えんとする姿で would make sense to me, but it's a bit confusing with the extra な. What is it? Can it be the perfective ぬ (as in 風が立ちぬ =The wind has risen)?