SAN ANTONIO - Part of Adolf Hitler's vision for the Third Reich was the Fuhrermuseum, which would be the centerpiece of a cultural district in Linz, Austria, a spectacular storehouse of the world's art. To fill his museum, Hitler directed his men to plunder millions of works of art from conquered countries. The incredible Goudstikker Gallery in Amsterdam was ransacked. A grouping of 45 important works, mostly Old Masters, restituted to the gallery's heirs goes on exhibit at the McNay Art Museum Wednesday.