As bar patrons this year ordered round after round of RumChata, a popular brand of a drink that combines rum and horchata, they brought life to a trademark battle.RumChata struggled to sell about 1 million bottles after it hit the market in 2009, said Thomas J. Maas, an associate at Katten, Muchin, Rosenman LLP, the son and grandson of part owners of RumChata.The fortune of the cream-colored, cinnamon-spiced drink with Spanish and Mexican influences changed this year.The company that makes the drink, Agave Loco LLC, plans …