Steps to Reproduce:

1. Create and start a sprint
   
2. Add Agile Sprint Health Gadget
   
3. Rename one of the user who is the assignee of an issue in that sprint
4. Re-assign the issue of that renamed user to someone else
5. Go back to the dashboard and there is an unknown avatar. Hovering on it shows the previous name of the renamed user
   

Expected Behaviour

• There shouldn't be an unknown avatar on the Agile gadget. It should only show the avatars of the assignee, regardless of whether the user has been renamed or not.

Actual Behaviour

• An unknown user avatar appears on the Agile gadget. Hovering on it shows the previous name of the renamed user

Environment

• Reproducible in JIRA 6.4.12 and Agile 6.7.1