[fix] queue_job: JobsTrap.perform_enqueued_jobs

Closes #651

queue_job/tests/common.py

@@ -228,12 +228,12 @@ def by_graph(job):
             return job.graph_uuid or ""
 
         sorted_jobs = sorted(self.enqueued_jobs, key=by_graph)
+        self.enqueued_jobs = []
         for graph_uuid, jobs in groupby(sorted_jobs, key=by_graph):
             if graph_uuid:
                 self._perform_graph_jobs(jobs)
             else:
                 self._perform_single_jobs(jobs)
-        self.enqueued_jobs = []
 
     def _perform_single_jobs(self, jobs):
         # we probably don't want to replicate a perfect order here, but at