'Error 500' appears if a user navigates to the deleted branch.

Precondition:
'Jcommune' user should exist.
Step to reproduce:
1. Navigate to the Pouple using admin/admin credentials
2. Navigate to the Jcommune - Forum Structure
3. Create New Section and New Branch
4. Add all needed permission for the 'Jcommune' user
5. Navigate to the Jtalks-Jcommune and go to the Branch from step 3
6. Add new topic
Note: Don't logout from the Jtalks-Jcommune
7. Navigate to the Pouple and delete Branch from step 3
8. On the Jtalks-Jcommune tab refresh the page

Actual: 'Error 500. Server encounters an error while processing your request. Please try to refresh this page later or go to forum main page' message appears
Expected: 'Error 404' message should appear.