Exit early when no results are returned from LRANGE given jobs might already processed

[vipulnsward]

Or a high load environment:

• The length is not guaranteed to be always as such
• Sidekiq can clear out some jobs
• We don't need to keep iterating if the jobs have already been cleared and there are no jobs
• This can be expensive operation to loop over unnecesarily

The other part of this is extra jobs added to the end of queue, but we can't safely predict that

(PS: My lua is weak, let me know better way if any :-) )