Bluesky accounts with image-only posts can be added to RSS Reader

Adding a Bluesky account to RSS Reader failed with "The Reader action failed" when one of its recent posts had no text, such as a post with only an image. Those posts are now titled "Post by" and the author's name. Feed entries without a title are named "Untitled entry", and a subscription that cannot be checked shows the reason beside it again instead of failing.