extra preconditions guard against a bug in dgrid reported: https://github.com/SitePen/dgrid/issues/752
extra preconditions
guard against a bug in dgrid
reported: https://github.com/SitePen/dgrid/issues/752

git-svn-id: 351b9af0f963dc927ffedc11baa804e1cafb7047@7206 463e38ab-4f4e-0410-907a-65d2b3888964

peopleware/js-ppwcode-vernacular-persistence,peopleware/js-ppwcode-vernacular-persistence