Don't extend release_download when none is set

couchpotato/core/plugins/renamer.py

@@ -204,6 +204,7 @@ class Renamer(Plugin):
         db = get_db()
 
         # Extend the download info with info stored in the downloaded release
+        if release_download:
             release_download = self.extendReleaseDownload(release_download)
 
         # Unpack any archives