Spots IOP: legacy_params(): adapt for latest mask changes

Shame on me, this should have landed before 1.6,
it was lying in load-raw-raw-data branch (PR #619) since at least Aug 5,
but i totally forgot about this particular commit...

Consequences:
for an image with spot v1, opened from mid summer until now:
	upgrade to v2 = results in broken mask
Now:
	upgrade to v2 = ok...

(cherry picked from commit fa36f88cad947f4860925b050399a341e8f7d72a)