Cannot subscribe to podcasts that have not been updated recently

[nsw42]

Trying to podcast-subscribe add fails if no new entries have been published for the podcast recently. The symptom is that podcast-subscribe add reports Did not find valid feed at <URL>.

Looks like a fix is as simple as editing subscribe.py (line 117) to test url_stats.doc.entries, rather than url_stats.entries.

(Eg at the time of writing, the most recent episode for https://podcasts.files.bbci.co.uk/b07dx75g.rss is dated 14 Feb 2023 - approx 6 months ago. The one-line fix to subscribe.py works for me)