Granting admin access to other users to workspaces converted from personal accounts is not working

Issue Summary

Adding a user to an Admin group on a workspace that was converted from personal accounts,  will not give those users Admin rights for that workspace. Users will not have permission to add new users, projects, or snippets for that workspace. 

The owner of the converted workspace is affected in a different way, as he/she will not be able to add himself/herself to any group under their workspace.
This will affect the "branch permission" and other features where the access is either granted or limited to a given group.

Steps to Reproduce

1. Create an administrator group into a workspace converted from a personal account and try to add users to this group, without success to add yourself.
2. Ask other users to perform actions that would require admin access to the workspace

Expected Results

The users should be able to perform changes that require admin access to the workspace
The owner of the workspace should be able to be listed as member of the groups that he administrates.

Actual Results

The users are not able to perform changes that require admin access to the workspace and will face a Permissions denied error.
The owner is not able to be listed as a member of the groups that he administrates.

Workaround

Create a new workspace,  different from the converted workspace, should work properly, allowing users in the Admin group to administer that workspace and for the workspace owner to be added to groups.