Bullet Ray Tracing errors for a DEM shape

[lwellerastro]

ISIS version(s) affected: 7.0.0, 7.1.0

Description
The following error is thrown by qnet when working with Kaguya TC images initialized with a DEM shape model:

My default IsisPreferences file includes the following:

Group = ShapeModel
  RayTraceEngine = Bullet
  OnError = Continue
EndGroup

I need to use this for the Phobos project since the data have been initialized with a DSK and I am working both projects concurrently. I can not comment out this section and work with the ISIS default ray tracing for Phobos due to problems with HRSC described in #5036. I must use isis7.1.0 for the Phobos project which contains this bug because the SRC camera model only exists in that version. I can not go back to isis7.0.0 where the bug does not exist since SRC will be unusable. So I have chosen to leave Bullet on all of the time thinking it was only invoked when working with a DSK shape file.

It is also not possible to specify a preference file for the interactive programs - they throw errors. I understand I can specify preference files for command line programs and will do so as necessary, but I will have to comment and uncomment the ShapeModel section in my preference file frequently in order to work on both of these projects until this is addressed. And I will have to remember to do so. If there is some other way to work around this problem please let me know.

I don't know specifically how the ray tracing engines work, but I thought they only applied to DSKs so it seems like a bug that the DEM is even being considered while Bullet is "on".

How to reproduce
Isis3Tests/RayTracing/ under my user work area contains a small list of images (which reside on /scratch) and a small associated network that will produce the above error when attempting to open in qnet. Any of the images in the list will throw a similar error if attempting to run campt or any isis program which needs to utilize a loaded shape model.