fix: fix for infinite recursion/deadlock for specific channels

this applies mainly for meta channels like UC4R8DWoMoI7CAwX8_LjQHig,
which ythdd can't parse and thus doesn't support

ythdd_inv_tl.py

@@ -771,7 +771,7 @@ def channels(data, req, only_json: bool = False):
 	verified     = False # to be replaced later with ythdd_extractor.isVerified(...)
 
 	author_name  = safeTraverse(channel_meta, ["title"], default="Unknown Channel")
-	author_ucid  = safeTraverse(channel_meta, ["externalId"], default="UNKNOWNCHANNELID")
+	author_ucid  = safeTraverse(channel_meta, ["externalId"], default=data[3]) # prevent recursion with fallback to provided ucid
 
 	ythdd_globals.general_cache["continuations"]["channels"][author_ucid] = {
 		"avatar": avatar,