Refs #10349 Check for partial group processing early

We don't want to do any loading/validation/autofilling before we've
checked for partial processing of a group/
" + ex.what(), "Error");
Refs #10349 Use a set of rows instead of vector

In this case, std::set is more appropriate than std::vector.
Merge branch 'feature/10349_stitch_processing_warning' into develop