37beac8eb8
Was happening when viewport visibility on the particle system is disabled.
This became an issue after c45afcf, but the actual issue goes a bit deeper
and the following aspects were involved:
- Relations builder for particle system was ignoring particle system if
it's visibility is not enabled for viewport. This is something what
shouldn't have been done -- depsgraph relations are supposed to be the
same no matter if it's viewport or render.
- Relation builder was only dealing with duplication set to object, but
was ignoring group duplication.
This is technically a regression in 2.79a-RC as well, so would need to
backport this fix to the branch after extra testing is done here in the
studio.