Merge pull request #15620 from djberg96/prefetch_below_threshold

Check for messages key in prefetch_below_threshold?
(cherry picked from commit 6e08686)

https://bugzilla.redhat.com/show_bug.cgi?id=1480629

app/models/miq_server/worker_management/dequeue.rb

@@ -61,7 +61,7 @@ def prefetch_stale_threshold
 
   def prefetch_below_threshold?(queue_name, wcount)
     @queue_messages_lock.synchronize(:SH) do
-      return false if @queue_messages[queue_name].nil?
+      return false unless @queue_messages.key_path?(queue_name, :messages)
       return (@queue_messages[queue_name][:messages].length <= (::Settings.server.prefetch_min_per_worker_dequeue * wcount))
     end
   end