3D render shows second component even with 0 opacity transfer function

[PaulHax]

Reproduce:

• With a 2 component image
• set one of the components opacity transfer function points to 0
• See the color map of the zeroed component tint the volume

With this test data:
http://localhost:8082/?rotate=false&image=test-data/HeadMRVolume2Components.nrrd

Expected no cyan in the image: