Administrator can remove last Owner of group if user is deactivated
### Summary
Administrator users are able to remove the last owner of a group if that user has been deactivated. This results in a group without an Owner.
### Steps to reproduce
1. Add a user as the only `Owner` for a group
2. Deactivate the user
3. Have an administrator user navigate to the group and remove the deactivated user with `Owner` permission
### What is the current *bug* behavior?
If the last `Owner` of a group is removed, the group is left without a user with `Owner` permission
### What is the expected *correct* behavior?
The last `Owner` of a group should not be able to be removed.
### Environment Information
User reported this on 14.6.1. I was able to replicate this on 14.0.12
### Links
Customer ticket: https://gitlab.zendesk.com/agent/tickets/275508 (internal use)
issue