m_has_rays in libs/rover/ray_generators/{ray_generator,camera_generator} issues

[brugger1]

I noticed there is a member m_has_rays in the ray_generator class. It is always set to false in camera_generator, which seems incorrect. I assume it should only be set to false if there are actually no rays generated. The only place m_has_rays is used is in RayGenerator::get_has_rays, which is never called in the entire code base.

Assuming this is an issue, either the function and variable can be removed or the code in camera_generator can be fixed. It should probably also be set in visit_generator.

I'm happy to fix if it is an issue and if we decide which of the two paths to take.