Bug 30974: Set size for indexing jobs to 1

Bug 30974: Set size for indexing jobs to 1

job's size is the number of records to index, but when finished the progress is always set to 1.

Wich leads to: finished 1/42

Test plan:
Don't apply this patch
Use the batch item modification tool to update more than 1 item
Notice that the new indexing job has a size of the number of items you
modified
When finished, the job detail shows "Finished. 1/X"
Apply this patch, repeat
Notice that now the progress shows 0/1 before the job is done, then 1/1
when finished

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>