Ensure that jsonindex count doesn't fail for zero results

[Paul Everitt]

Partial traceback:

 File "/srv/karlstaging/staging/51/eggs/karl-4.25.1-py2.7.egg/karl/views/people.py", line 764, in recent_content_view
   principals=effective_principals(request),
 File "/srv/karlstaging/staging/51/eggs/karl-4.25.1-py2.7.egg/karl/views/batch.py", line 81, in get_pg_batch
   return get_searcher_batch(searcher, context, request, kw)
 File "/srv/karlstaging/staging/51/eggs/karl-4.25.1-py2.7.egg/karl/views/batch.py", line 56, in get_searcher_batch
   total, batch = searcher(context, request, kw, batch_start, batch_size)
 File "/srv/karlstaging/staging/51/eggs/karl-4.25.1-py2.7.egg/karl/views/batch.py", line 79, in searcher
   context._p_jar, query, kw, batch_start, batch_size)
 File "/srv/karlstaging/staging/51/eggs/j1m.relstoragejsonsearch-0.2.1-py2.7.egg/j1m/relstoragejsonsearch/search.py", line 116, in search_batch
   return count, result
UnboundLocalError: local variable 'count' referenced before assignment