NEWLYWEDS Julia Roberts and Lyle Lovett have said ''I do'' for a second time. Roberts and Lovett enjoyed it the first time around so much that they got married again before more than 30 celebrity friends at a trendy Hollywood restaurant. Lovett gave Roberts a diamond-encrusted gold ring as the preacher declared them married again and friends applauded. Among the guests were Julia's Pelican Brief co-star Denzel Washington and Nick Nolte. After the vows, the party began with the pair's friends feasting on all the pizza and champagne they could eat and drink. ''They drank lots of champagne - Perrirt Jouet Grand Brut and Moet et Chandon Brut Imperial - I had to order extra bottles especially for them,'' said the manager of the Tutto Bene restaurant, Christine Herledan.