Peeled images: different distances requested, all images same

[tbowers7]

Using the paper-galaxy-rt-model setup, I requested multiple peeled images, all identical except for the distance range (image.set_depth()). When successive images are less restrictive than the previous (i.e. first image: 0-4kpc, second image: 0-8kpc, etc.), all output images are identical, and equal to the first (i.e. most restrictive) case. However, when successive images are more restrictive than the previous, this issue does not arise, and individual peeled images correspond to the requested distances.

[astrofrog]

Thanks for fixing this in #22!