[arte] fix bug when date is not available
[arte] fix bug when date is not available

sputnick-dev/weboob,willprice/weboob,willprice/weboob,nojhan/weboob-devel,laurent-george/weboob,laurent-george/weboob,RouxRC/weboob,RouxRC/weboob,sputnick-dev/weboob,nojhan/weboob-devel,sputnick-dev/weboob,nojhan/weboob-devel,laurent-george/weboob,willprice/weboob,RouxRC/weboob