JOSM/CommandLine: fix exception after JOSM update

git-svn-id: http://svn.openstreetmap.org/applications/editors/josm/plugins@29780 b9d5c4c9-76e1-0310-9c85-f3177eceb1e4
fix after JOSM update

git-svn-id: http://svn.openstreetmap.org/applications/editors/josm/plugins@29782 b9d5c4c9-76e1-0310-9c85-f3177eceb1e4
[josm_plugins]: use new core function for default menu position (see #josm8900)

git-svn-id: http://svn.openstreetmap.org/applications/editors/josm/plugins@29784 b9d5c4c9-76e1-0310-9c85-f3177eceb1e4