s2050, t7919: correctly flags duplicate link during add
s2050, t7919: correctly flags duplicate link during add

opencadc/vosui,opencadc/vosui,opencadc/cadc-vosui,hjeeves/cadc-vosui,opencadc/vosui,hjeeves/cadc-vosui,opencadc/vosui,opencadc/cadc-vosui,hjeeves/cadc-vosui,opencadc/cadc-vosui,opencadc/cadc-vosui,hjeeves/cadc-vosui