NEW YORK — When John Cage and Morton Feldman, experimental composers of contrasting styles but compatible temperaments, met in the Carnegie Hall lobby on Jan. 26, 1950, it began a lasting association. Their chance encounter came full circle in 2001, when vocalist and composer Joan La Barbara initiated “When Morty Met John,” a three-year cycle of Carnegie Hall concerts devoted to Cage, Feldman and their colleagues of the New York School, including Earle Brown and Christian Wolff.