NEWARK, N.J. — Actor-comedian Tracy Morgan and other people in a limousine struck from behind by a Wal-Mart truck on a highway in June are at least partly to blame for their injuries because they weren’t wearing seatbelts, the company said in a court filing Monday. The filing was made in federal court in response to a lawsuit Morgan filed in July over the accident, which killed his friend James McNair, who was accompanying the former “Saturday Night Live” and “30 Rock” star back from a show in Delaware.