Jim Broadbent and Lindsay Duncan confront the state of their sagging marriage in this Hanif Kureishi-penned drama. But how depressed is it supposed to make us?It should in theory be possible to make a movie about a couple who make a sentimental journey to Paris to celebrate their 30th wedding anniversary, only to discover over 48 unforgettable hours that they are entirely content with each other. That isn't what…