Typo in postmap handling
Typo in postmap handling

Without this fix an empty postmap_task causes an assertion failure in
physical_perform_updates, because it finds targets.empty().

StanfordLegion/legion,StanfordLegion/legion,StanfordLegion/legion,StanfordLegion/legion,StanfordLegion/legion,StanfordLegion/legion,StanfordLegion/legion,StanfordLegion/legion