Make sure all possible status are always returned

It makes it harded to parse the API response if you always have to check
if 'deleted' is set and if what value it has. I think to simply return 0
for all status value is good practice.

ckanext/harvest/logic/dictization.py

@@ -37,7 +37,7 @@ def harvest_job_dictize(job, context):
             func.count(HarvestObject.id).label('total_objects'))\
                 .filter_by(harvest_job_id=job.id)\
                 .group_by(HarvestObject.report_status).all()
-        out['stats'] = {}
+        out['stats'] = {'added': 0, 'updated': 0, 'errors': 0, 'deleted': 0}
         for status, count in stats:
             out['stats'][status] = count