When a perforce commit is amended to add a job id, the job ID is not picked up by a partial re-index

When a perforce commit is amended to add a job id, the job ID is not properly recognised by a partial re-index.

Steps to reproduce:
1. create a JIRA issue which is linked to a P4 job ID using the JFP's perforce integration
2. submit a perforce changeset with no attached job id's
3. wait for fisheye to index the changeset
4. edit the changeset in perforce to add the job id
5. perform a partial re-index of a changeset range which includes the amended changeset

The perforce job ID will be visible when directly viewing the changeset in fisheye, but will not be returned by the REST endpoint, for example:
http://localhost:6060/foo/rest-service-fe/changeset-v1/listChangesets?rep=PS&expand=changesets[-21:-1].revisions[0:29]&comment=PS-3&p4JobFixed=PS-3

The changeset will then not be visible in the source tab in JIRA.

Jobs are re-index properly when doing a full repository re-index.