This is a milestone of sorts, no matter what you think of the subject. Tonight’s The Carmichael Show, which is making a point this season of becoming known for being an issues-oriented sitcom, tonight takes on the issue of fallen idols – and the specific subject is Bill Cosby. Considering how Cosby, for NBC, not only made racial history with I Spy in the 1960s by becoming the first African-American to star in a drama series, but his The Cosby Show in the 1980s virtually saved the sitcom, and NBC’s fortunes, almost singlehandedly. So this show tonight may be very funny, and may even be bold – but one thing it’s not, just for the record, is grateful. Not that it should be…