handly empty subs

ox/web/youtube.py

@@ -105,6 +105,7 @@ def info(id, timeout=cache_timeout):
                 if not duration:
                     duration = '2'
                 end = start + float(duration)
+                if t.firstChild:
                     text = t.firstChild.data
                     subs.append({
                         'in': start,