Images break on some feeds in web client but load in third-party apps

[lilacpixel]

I've found that there are a small number of feeds in which images don't load properly in the Miniflux web client, while the same images load just fine when viewed through third-party clients (such as NetNewsWire).

When testing an image URL from one of the feeds using curl, I found that passing no headers returned a 404, while passing the referer header for the originating domain returned the correct image. I didn't have any luck trying to add that referer to internal/reader/rewrite/rules.go, as in c384f96. So I do suspect a referer issue, but I'm not sure what I might have overlooked, or why it might be working in NetNewsWire as is.

Examples of feeds where images do not load in the web client:

• https://www.parkablogs.com/rss.xml
• All RSS feeds on xcancel.com (i.e. https://xcancel.com/[username]/rss)

Thanks for taking a look!