IF you like to spice your theatergoing with a dash of mystery and danger, Ernie Curcio's double-bill of Unfinished and Sundrops is just the ticket. Finding the Katherine Gianaclis Park for the Arts involves locating an unmarked parking lot on an unlit side street. Follow a winding path and you're at the back of a deceptively small house, beneath the seedy ramparts of Sportsman's Royal Manor. That is the gateway to a ramshackle labyrinth at the terminus of which is not a Minotaur, but a black-box theater.