Crop poly error when 1 single pixel width

[dvezinet]

Minimum working example:

conf = tf.load_config('SPARC')

coll = tf.data.Collection()

coll.add_mesh_2d_rect(key='mRZ', res=0.005, crop_poly=conf)

Solution:

The algorithm currently only uses knots, this should be relatively easy to solve if we also use information about the centers, TBD