thrimshim: Fix bug where description playlists header was added with zero playlists

We only want it to show at all if there's at least one playlist.

thrimshim/thrimshim/main.py

@@ -292,9 +292,11 @@ def update_row(ident, editor=None):
 
 	# Include headers and footers
 	new_row['video_title'] = app.title_header + new_row['video_title']
+	description_lines = []
+	if playlists:
 		# NOTE: If you change this format, you need to also change the regex that matches this
 		# on the GET handler.
-	description_lines = [DESCRIPTION_PLAYLISTS_HEADER]
+		description_lines.append(DESCRIPTION_PLAYLISTS_HEADER)
 		description_lines += [
 			"- {} [https://youtube.com/playlist?list={}]".format(playlist.name, playlist.playlist_id)
 			for playlist in playlists