FIX: version check job when no versions are returned in json

lib/discourse_updates.rb

@@ -80,6 +80,7 @@ module DiscourseUpdates
         $redis.del(missing_versions_list_key)
       end
 
+      if versions.present?
         # store the list in redis
         version_keys = []
         versions[0,5].each do |v|
@@ -88,7 +89,9 @@ module DiscourseUpdates
           version_keys << key
         end
         $redis.rpush missing_versions_list_key, version_keys
-      versions
+      end
+
+      versions || []
     end
 
     def missing_versions