catmaid_get_connector_table can return duplicate rows

[jefferis]

There was a logic bug when handling a case where the same connector had >1 connection between the same pair of partner neurons.

aspgl_conn_T.in= catmaid_get_connector_table('aSP-g L', direction = 'in')
> table(duplicated(aspgl_conn_T.in))

FALSE  TRUE 
 3546   156 

Sample of the duplicate rows:

> aspgl_conn_T[34:35,]
   connector_id    skid      x      y      z confidence user_id partner_treenode_id                    last_modified partner_skid direction  dupl
34      5411498 1064687 417190 122158 114200          5     121             8322046 2017-01-31T10:17:02.947526+00:00      1273130  incoming FALSE
35      5411498 1064687 417190 122158 114200          5     121             8322046 2017-01-31T10:17:02.947526+00:00      1273130  incoming  TRUE