This commit fixes a bug when sparse groups are in use. Since sparse
group do not actually increment the reference counts of any procs
(they just retain the parent group) it is wrong to decrement the
reference counts of all procs in the group using
ompi_group_decrement_proc_count(). This commit makes the call to
ompi_group_decrement_proc_count() conditional on the group being
dense.
Fixesopen-mpi/ompi#1593
Signed-off-by: Nathan Hjelm <hjelmn@lanl.gov>