trac #5654 Handle an NPE (reason not identified, not able to reproduce)

git-svn-id: http://svn.openstreetmap.org/applications/editors/josm/plugins@29668 b9d5c4c9-76e1-0310-9c85-f3177eceb1e4
#7009 remove layer if WMS interface setup fails to find commune/departement

git-svn-id: http://svn.openstreetmap.org/applications/editors/josm/plugins@29669 b9d5c4c9-76e1-0310-9c85-f3177eceb1e4