Fix: don't show RSS sidebar link unless we have a RSS feed URL
Fix: don't show RSS sidebar link unless we have a RSS feed URL

If we enable the RSS sidebar link, it would always be displayed, even if
we don't actually have a RSS link for the current page.

This is noticeable on article pages, they don't have a .RSSLink, and the
RSS icon would still show.

Signed-off-by: Pedro Melo <3e267facec158a22a232125c74f1f09bceb68aac@simplicidade.org>

enten/hyde-y,enten/hyde-y