NEW YORK — A slain young NYPD officer was remembered for his ever-present smile and love of the job Friday at a packed St. Patrick’s Cathedral funeral where his sobbing widow shared the sad details of their last day together. On a snowy Manhattan day of mourning and heartache, New York Police Department Officer Jason Rivera was fondly recalled in eulogies as a man who followed his dreams into the department before his weeping spouse of three months recounted how the couple argued only hours before his fatal shooting inside a Harlem apartment. When the 22-year-old Rivera offered to drive her ho…