[arte] do not crash if 'VDA' fiels is missing in json

modules/arte/browser.py

@@ -182,6 +182,7 @@ class ArteBrowser(BaseBrowser):
         video.set_empty_fields(NotAvailable, ('url',))
         if 'VDE' in item:
             video.description = u'%s' % item['VDE']
+        if 'VDA' in item:
             m = re.match('(\d{2})\s(\d{2})\s(\d{4})(.*?)', item['VDA'])
             if m:
                 dd = int(m.group(1))