Handle the case when no complete queries exist in the grid walker.

When walking an empty grid, no queries for either complete or disjoint are
generated.  Disjoint handled this fine, but complete did not.  Fix this.

git-svn-id: https://groke.mcmaster.ca/svn/grad/colin/branches/TableTool_javization@10665 57e6efec-57d4-0310-aeb1-a6c144bb1a8b