fix #8692 - Handle null DeleteCommands in JoinAreaAction and ImproveWayAccuracyAction

git-svn-id: http://josm.openstreetmap.de/svn/trunk@5947 0c6e7542-c601-0410-84e7-c038aed88b3b
fix #8693 - CCE in Search Dialog caused by r5886

git-svn-id: http://josm.openstreetmap.de/svn/trunk@5948 0c6e7542-c601-0410-84e7-c038aed88b3b