Fix handling of sample_info/sample_pos for non-MSAA rasterizer
Fix handling of sample_info/sample_pos for non-MSAA rasterizer

* Refs #1025 but is not a complete fix as sample evaluation is still not
  working.
googlestadia/renderdoc,Zorro666/renderdoc,TurtleRockStudios/renderdoc_public,Zorro666/renderdoc,googlestadia/renderdoc,baldurk/renderdoc,Zorro666/renderdoc,googlestadia/renderdoc,TurtleRockStudios/renderdoc_public,googlestadia/renderdoc,googlestadia/renderdoc,TurtleRockStudios/renderdoc_public,Zorro666/renderdoc,TurtleRockStudios/renderdoc_public,baldurk/renderdoc,TurtleRockStudios/renderdoc_public,baldurk/renderdoc,Zorro666/renderdoc,TurtleRockStudios/renderdoc_public,baldurk/renderdoc,baldurk/renderdoc,Zorro666/renderdoc,baldurk/renderdoc,googlestadia/renderdoc