Conversion from spectral samples to RGB is incorrect

[vilya]

For example, when loading the eta spectrum for aluminium (spds/Al.eta.spd in the pbrt-v3-scenes collection) and converting it to RGB:

• pbrt-v3 produces {1.653941, 0.878499, 0.520123}
• minipbrt produces {37606.5, -11248.4375, 645.807739}