When celebrities go to a big-time bridal designer for their wedding dress, the one-of-a-kind dress they walk down the aisle wearing usually starts as an existing silhouette that the designer updates with elements from other gowns. It seems like that was the case with Jamie Chung's wedding dress. (She and longtime boyfriend Bryan Greenberg were married on Halloween, if you missed the news.) The Once Upon a Time actress wore a long-sleeve Monique Lhuillier wedding dress that looked—up top…