Update calling code in OpticalFlow.java to compute nadir_pXpYD once and
render two passes when either nadir_gen or nadir_undistort is enabled:
- nadir_gen=true  → renderNadirSequence(..., false) → *-NADIR-MERGED
- nadir_undistort=true → renderNadirSequence(..., true)  → *-NADIR-MERGED-RECTILINEAR

The nadir_pXpYD array is deep-copied per scene for the undistort pass so
the original sensor-coordinate data is preserved for the non-undistorted pass.
Co-authored-by: Claude <claude@elphel.com>