TerrainAnalysis.deygout_diffraction/2 short-circuits to integer 0
when the path has no interior points or the principal edge nu is
below the shadow boundary, which then made Float.round/2 blow up
inside compute_loss_budget when the rest of the losses were all
floats. Multiply the diffraction value by 1.0 before it feeds into
the total so clear paths coerce cleanly without touching
TerrainAnalysis's (number()) contract.
Graham McIntire
263c1bbdf5