A seaplane pilot and his passenger had to be rescued from the East River Saturday in Queens after their craft briefly took off — but then crashed after it was struck by a wave which cracked the windshield, the pilot and authorities said. The aircraft was near Riverside Drive and 158th St. in Whitestone, near the Throggs Neck Bridge, when the incident happened around 9:20 a.m., an FDNY spokesman said. A private boater who was nearby rescued the two people, who were not seriously hurt, from the