Random channels…. So Joan Rivers could use a new job (see page 28). I think she’s ready for prime time. Surely she could get a part on Growing Pains with Alan Thicke…. For the record: Cosby’s season-ender, filled with pompous speeches at fictional Hillman College, was self-indulgent, boorish and utterly un-entertaining. Cosby may be the king of TV, but he’s not perfect…. A chicken-or-egg question: Which got boring first, MTV or Miami Vice?…And speaking of dull, here’s the week on TV….