LONDON (Reuters) – An early work by British artist David Hockney, a painting depicting his well-known pool motif and not seen in public for more than 40 years, is headed for auction with an estimate of around $20 million. Hockney, 86, painted “California”, showing two naked figures in an outdoor swimming pool, in 1965 after his first trip to Los Angeles and it has been held in a private collection since 1968. The painting, last seen in public in 1979, is a highlight of auction house Christie’s “20th/21st Century: London Evening Sale” on March 7. It is listed with “a price on request”, with an …