jqueue: Don't return negative number for unchecked jobs when archiving

When the queue was empty, the calculation for unchecked jobs while
archiving would return -1. ``last_touched`` is set to 0, the job ID list
(``all_job_ids``) is empty. Calculating ``len(all_job_ids) -
last_touched - 1`` resulted in -1.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>

lib/jqueue.py

@@ -1321,7 +1321,7 @@ class JobQueue(object):
     all_job_ids = self._GetJobIDsUnlocked(archived=False)
     pending = []
     for idx, job_id in enumerate(all_job_ids):
-      last_touched = idx
+      last_touched = idx + 1
 
       # Not optimal because jobs could be pending
       # TODO: Measure average duration for job archival and take number of
@@ -1351,7 +1351,7 @@ class JobQueue(object):
     if pending:
       archived_count += self._ArchiveJobsUnlocked(pending)
 
-    return (archived_count, len(all_job_ids) - last_touched - 1)
+    return (archived_count, len(all_job_ids) - last_touched)
 
   @staticmethod
   def _GetJobInfoUnlocked(job, fields):