im_cull: fix the integer point branch

One wrangle wrote _threshold and the next read threshold, so the
comparison was always against 0, and the custom range multiplied by a
thresholdy parm that does not exist. Mirror the primitive branch: promote
the attribute's max to _filter_range_max, scale by it, read _threshold.
Both branches now delete the two temporaries.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

 otls/sop_lsgalante.im_cull.1.0.hdalc | Bin 14009 -> 12872 bytes
 1 file changed, 0 insertions(+), 0 deletions(-)

diff --git a/otls/sop_lsgalante.im_cull.1.0.hdalc b/otls/sop_lsgalante.im_cull.1.0.hdalc
index 6bb64cb..ed5c725 100644
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