[442761] Add comment about regression due to commit 1077eea

Add comment to ArrangeBorderedNodesAction#calculateEnabled() in order to
alert about the regression due to commit 1077eea.  
 
Change-Id: I7f8da055c71f3ef8ab6cbb391d7bd585413771b3
Signed-off-by: Mickael LANOE <mickael.lanoe@obeo.fr>