Lack of a topic description prevents the RSS feed from being generated

[jonathanmtran]

Describe the bug
When a topic is not given a description and the "Offer Public RSS" checkbox is checked, the feed URL results in a 500 error

To Reproduce
Steps to reproduce the behavior:

1. Add a new topic without a description and check the "Offer Public RSS" checkbox
2. Go to the user-facing interface and click the RSS icon for the topic created in step 1

Expected behavior
An RSS feed

Stacktrace
No stacktrace, but you'll see the following in the log (Campus Spotlight was the topic in question at our institution)

WARN [http-apr-4443-exec-9] servlet.RssFeedController.[] 2018-08-28 11:44:09,458 - Failed to create SyndFeedOutput for topic 'Campus Spotlight'