Fix subscription checking breaking due to workers crashing

The try statement was missing an except clause. So if there
was an exception such as the tor browser being closed or
getting a 429 error during the request, the workers would
crash until there were none left to handle checking.

youtube/subscriptions.py

@@ -319,6 +319,8 @@ def check_channel_worker():
         channel_id = check_channels_queue.get()
         try:
             _get_upstream_videos(channel_id)
+        except Exception:
+            traceback.print_exc()
         finally:
             checking_channels.remove(channel_id)