The 10-day Venice Film Festival began glamorously enough last week, with Scarlett Johansson and Miuccia Prada swirling through the opening dinner in a tent parked on the Lido’s beach. But not even Friday’s amFAR party attended by Margherita Missoni could top Saturday night’s candlelit dinner, held in the courtyard of the Doges’ Palace after the premiere of “Merchant of Venice.” Newcomer Lynn Collins, who plays Portia, made her way from the Lido to the dinner just as the bell tower at Saint Mark’s struck midnight. The evening left Collins, dressed in a scarlet red dress by Giorgio Armani, too overwhelmed for words. What did she think of dining at the palace? “It’s amazing,” she said, her eyes welling up with tears.