[Mixcloud] Harmonize ID generation from lists with full ID generation

Mixcloud IDs are generated as `username_slug` when the full ID dict has been
downloaded.  When downloading a list (e.g. uploads, favorites, ...), the temporary
ID is just the `slug`.  This made e.g. archive file usage require the download
of stream metadata before the download can be rejected as already downloaded.

This PR attempts to get the uploader username during the GraphQL query, so the
temporary IDs are generated similarly.

youtube_dl/extractor/mixcloud.py

@@ -251,8 +251,12 @@ def _real_extract(self, url):
                 cloudcast_url = cloudcast.get('url')
                 if not cloudcast_url:
                     continue
+                video_id = cloudcast['slug']
+                owner_username = try_get(cloudcast, lambda x: x['owner']['username'], compat_str)
+                if owner_username:
+                    video_id = '%s_%s' % (owner_username, video_id)
                 entries.append(self.url_result(
-                    cloudcast_url, MixcloudIE.ie_key(), cloudcast.get('slug')))
+                    cloudcast_url, MixcloudIE.ie_key(), video_id))
 
             page_info = items['pageInfo']
             has_next_page = page_info['hasNextPage']
@@ -321,7 +325,8 @@ class MixcloudUserIE(MixcloudPlaylistBaseIE):
     _DESCRIPTION_KEY = 'biog'
     _ROOT_TYPE = 'user'
     _NODE_TEMPLATE = '''slug
-          url'''
+          url
+          owner { username }'''
 
     def _get_playlist_title(self, title, slug):
         return '%s (%s)' % (title, slug)
@@ -345,6 +350,7 @@ class MixcloudPlaylistIE(MixcloudPlaylistBaseIE):
     _NODE_TEMPLATE = '''cloudcast {
             slug
             url
+            owner { username }
           }'''
 
     def _get_cloudcast(self, node):