By Alek Arend Over the last two years the Las Vegas Raiders had one of the strongest quarterback rooms in the NFL. Derek Carr was the starter and former Heisman winner Marcus Mariota served as backup. Now that Mariota is off to the Falcons, the Raiders need a new backup. On Friday morning the Las Vegas Raiders reportedly signed veteran backup Nick Mullens. He’ll compete for the team’s backup quarterback position against Garrett Gilbert. Nick Mullens is no star, but he’s an experienced backup. He’s thrown for 4,861 yards and 26 touchdowns with 22 picks, going 5-12 in starts, over the last four …