[dropbox] Fix the video url query (fixes #3868)

Previously it would convert urls without a query into 'something.mp4&dl=1'

diff --git a/youtube_dl/extractor/dropbox.py b/youtube_dl/extractor/dropbox.py
index 817a9bd6143544560541dbdb1c2d1ea18b95177d..5f24ac7214a95b762d3805779d1c9517ca3d0000 100644 (file)
--- a/youtube_dl/extractor/dropbox.py
+++ b/youtube_dl/extractor/dropbox.py
@@ -29,9 +29,8 @@ class DropboxIE(InfoExtractor):
         video_id = mobj.group('id')
         fn = compat_urllib_parse_unquote(url_basename(url))
         title = os.path.splitext(fn)[0]
-        video_url = (
-            re.sub(r'[?&]dl=0', '', url) +
-            ('?' if '?' in url else '&') + 'dl=1')
+        video_url = re.sub(r'[?&]dl=0', '', url)
+        video_url += ('?' if '?' not in video_url else '&') + 'dl=1'
 
         return {
             'id': video_id,