[josm_openinghours] code cleanup

git-svn-id: http://svn.openstreetmap.org/applications/editors/josm/plugins@30116 b9d5c4c9-76e1-0310-9c85-f3177eceb1e4
[josm_openinghours] fix #7903 - ArrayIndexOutOfBoundsException in unknown conditions. IllegalArgumentException will be thrown earlier if reproduced.

git-svn-id: http://svn.openstreetmap.org/applications/editors/josm/plugins@30117 b9d5c4c9-76e1-0310-9c85-f3177eceb1e4