7063: endless loop in probably_alive_range

Port from gramps34 branch my fix after retest by the bug submitter.

    Add a hack protection for descendants like we already have
    for ancestors, and add a debug printout.

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/branches/maintenance/gramps40@23161 4ae1f11a-8b86-4847-b8af-ab372f36d1fd