Imagine Isabelle Huppert as a Euro ‘American Idol’ star turned factory worker. It’s ‘Souvenir’

Isabelle Huppert as a has-been chanteuse is all a film fan should need to stoke the wanna-see factor for “Souvenir,” and it probably doesn’t hurt that there’s a May-December romance as an extra incentive for devotees of the magnetic French superstar.

But promise is all one’s left with after Belgian…