Remove handle only when the job is done

This commit stops the client from removing the job handle from
client.jobhandlers when the worker has sent an update (e.g. WORK_STATUS)
without terminating its life.

WORK_DATA       |
WORK_WARNING    | => Notification
WORK_STATUS     |

WORK_COMPLETE   |
WORK_FAIL       | => Notification + End of life
WORK_EXCEPTION  |