Stop unassigning agent when you change the team.

Please keep the assignee when you change the team for a conversation. If the assignee is still in the group that is being changed to, there’s no reason to unassign them everytime. 

For example, if I switch the Team Inbox, the assignee is removed from the conversation, and then you have to reassign it. 

This also affects reporting metrics. Looking like more assigning and change of assignment is happening than what is actually happening.