Volumes with a single value incorrectly read

[d-chagnon]

Hello,
Having a volume with a single real value, but a range of possible voxel values can't be read correctly because the real_value_scale is not allowed to have a value of 0 here. A way to reproduce that issue is to, for example, create a volume using:
make_phantom -signed -short -voxel_range -10 100 <template_volume>
minccalc -expression '1' <template_volume> <test_volume>
which yields a test_volume filled with 1s, but with a voxel values that can range from -10 to 100. Calling mincbbox on that volume returns "X X X -inf -inf -inf" where X is 1.8E308.
As far as I can tell solving this would only require removing the lines I linked from set_volume_real_range, but I don't know if those were added to fix something else.

[gdevenyi]

Sadly, the commit that added this code was mixed in with some other code and the message doesn't give any hints as to why:
7c22f97