“Dys-FUNK-tional” muttered my guest halfway through this tedious and utterly un-funky biographical jukebox musical about Chaka Khan, and I nearly surrendered my job to him then and there. The show augments the lauded singer’s scattered hits from the 70s onwards – Tell Me Something Good, I Feel For You, Ain’t Nobody – with work from other artists: this soundtrack is shackled to a by-the-numbers tale of triumph over adversity and addiction.