Things are rarely easy for the actor who choses to dabble in pop. For every Donald Glover, apparently able to flit at will between the film set and the recording studio, pausing only to bask in the superlatives that garland both sides of his work, there are umpteen Russell Crowes or Johnny Depps, their dreams of polymath stardom crushed by a reception that ranges from suspicion to bemusement to outright hostility.