Fix single plane ND2 line scan (rebased onto develop)



This is the same as gh-1085 but rebased onto develop.

----

This should resolve the issue in https://trac.openmicroscopy.org.uk/ome/ticket/12222; no other files should be affected.  Verifying that the QA image when opened in ImageJ or imported into OMERO matches the description in the ticket is sufficient.