message: Use surface_interaction flag to check for emission
diff: #include <visionaray/get_surface.h>
  #include <visionaray/result_record.h>
  +#include <visionaray/surface_interaction.h>
  #include <visionaray/traverse.h>
  namespace visionaray
  @@ -85,7 +86,7 @@ struct kernel
  auto src = surf.sample(view_dir, refl_dir, pdf, inter, gen);
  auto zero_pdf = pdf <= S(0.0);
  - auto emissive = has_emissive_material(surf);
  + auto emissive = inter == I(surface_interaction::Emission);
  dst = mul( dst, src, active_rays && !zero_pdf, dst );
  dst = select( zero_pdf && active_rays, C(0.0), dst );
  