Avoid crashing when feedjira fails to parse xml feed (#3376)

Fixes #3371

Signed-off-by: George Araújo <george.gcac@gmail.com>

_plugins/external-posts.rb

@@ -25,7 +25,12 @@ module ExternalPosts
     def fetch_from_rss(site, src)
       xml = HTTParty.get(src['rss_url']).body
       return if xml.nil?
-      feed = Feedjira.parse(xml)
+      begin
+        feed = Feedjira.parse(xml)
+      rescue StandardError => e
+        puts "Error parsing RSS feed from #{src['rss_url']} - #{e.message}"
+        return
+      end
       process_entries(site, src, feed.entries)
     end