Speculatively fix another bug involving deleting invalid handles.

If this handle is deleted, make sure to mark it as such.  Otherwise,
there seems to be a double delete occuring and causing issues.


git-svn-id: https://groke.mcmaster.ca/svn/grad/colin/trunk/TableTool@8511 57e6efec-57d4-0310-aeb1-a6c144bb1a8b