Updates Dispatcher to address PR feedback

Addresses PR feedback where the previous changes could result in a
degredation of services. This commit returns the orignal Dispatcher
looping behavior.

Author: hms

lib/solid_queue/dispatcher.rb

@@ -25,7 +25,7 @@ def metadata
       def poll
         batch = dispatch_next_batch
 
-        batch.size < batch_size ? polling_interval : 0.seconds
+        batch.size.zero? ? polling_interval : 0.seconds
       end
 
       def dispatch_next_batch