elfeed--atom-content: use 'summary' if there is no 'content'

[blbelew]

Some atom feeds, notably GitLab's project activity feeds (project.atom) include a summary tag but no content tag. Fall back to using the summary as the content if there is no content.

[Thaodan]

I don't think this a good change. If there is no content it should not be shown as such but as summary.

[blbelew]

The gitlab project.atom feeds show activity on any project you are subscribed to with gitlab. The way they are formatted, the "content" of the entry is entirely in the summary tag. Elfeed isn't showing that at all right now - so it doesn't display anything at all for the body of the entry. It makes sense that if if there is no content tag, but there is a summary tag, that we at least show that instead of nothing at all.

[Thaodan]

I get that but putting the summary into the content tag makes it harder to detect if there is actual content. Further what if there's a summary and content?