Items are being duplicated if their URL changes
If a channel provider changes the URLs that the items point to (like changing `http` to `https` in URLs), the items get duplicated.
Observe such a feed.
Items' URLs are silently updated.
New items are added.
Built with Qt 5.12.2, running with Qt 5.12.2
Running on: Gentoo/Linux x86_64 4.12.12-gentoo #1 SMP Sun Oct 1 18:31:38 EDT 2017