Authorize all teams to admin: fix 500 error on showing team page.

500 error was occured in the following steps:

1. user1 creates new team "team1".
2. Assign team1 to project1.
3. Sign in as admin. This admin is not a member of team1.
4. Open project1 team setting page (/project1/team).
5. Click "team1" link in "Assigned teams" area.
6. 500 error.

Fixed this issue.
Merge pull request #4206 from babatakao/authorize_all_teams_to_admin

Authorize all teams to admin: fix 500 error on showing team page.