jqueue: Don't return negative number for unchecked jobs when archiving
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 <68b67885ff74281219b4a4be33cc20fd45078d7c@google.com>
Reviewed-by: Iustin Pop <acf83a5274f31a43af6b914614365999469c1a31@google.com>

andir/ganeti,onponomarev/ganeti,mbakke/ganeti,onponomarev/ganeti,mbakke/ganeti,yiannist/ganeti,apyrgio/snf-ganeti,andir/ganeti,apyrgio/snf-ganeti,apyrgio/ganeti,ganeti/ganeti,leshchevds/ganeti,ganeti/ganeti,grnet/snf-ganeti,bitemyapp/ganeti,ganeti/ganeti,dimara/ganeti,yiannist/ganeti,ganeti-github-testing/ganeti-test-1,leshchevds/ganeti,dimara/ganeti,mbakke/ganeti,bitemyapp/ganeti,andir/ganeti,apyrgio/ganeti,ganeti-github-testing/ganeti-test-1,yiannist/ganeti,grnet/snf-ganeti,leshchevds/ganeti