CHICAGO — Matt Nagy is as excited as the Chicago Bears fanbase about the debut of rookie quarterback Justin Fields — aka the franchise savior — in the preseason opener Saturday against the Miami Dolphins at Soldier Field. The game only will amplify the question everyone has been asking for months: Is there a path for Fields to be the starter when the season kicks off Sept. 12 against the Los Angeles Rams in Inglewood, Calif.? Veteran Andy Dalton, who according to Nagy has aced the test of mastering the offense, will start against the Dolphins and is expected to play briefly. Fields will enter,…