Do not scale down workers if there are more than one working worker.

When after_perform_scale_down is called it will always have at least one working worker, which is itself, but it may have more workers working.

We can't just scale down based on the number of pending jobs, because if multiple jobs are queued at the same time and we have this many number of workers, we may have many working jobs and no pending job, yet we can't kill those workers.

By checking if there are any working workers besides the job itself we prevent this from happening.

lib/heroku-resque-auto-scale.rb

@@ -16,12 +16,17 @@ def workers=(qty)
       def job_count
         Resque.info[:pending].to_i
       end
+
+      def working_job_count
+        Resque.info[:working].to_i
+      end
     end
   end
 
   def after_perform_scale_down(*args)
-    # Nothing fancy, just shut everything down if we have no jobs
-    Scaler.workers = 0 if Scaler.job_count.zero?
+    # Nothing fancy, just shut everything down if we have no pending jobs
+    # and one working job (which is this job)
+    Scaler.workers = 0 if Scaler.job_count.zero? && Scaler.working_job_count == 1
   end
 
   def after_enqueue_scale_up(*args)