Application on index page will not load, if something in 'site.db' is wrong

[ChristianLutzCL]

Describe the bug
After setup or if you create a new database file (site.db), the application won't work.

To Reproduce
Steps to reproduce the behavior:

1. Setup project or regenerate site.db file
2. Run application
3. Open website and see the error

Expected behavior
Index page should display without any checked websites

Additional context
The solution to this problem is already known.
The main route queries trough the database without checking if there is something in the database.
A simple check for the case of an empty table would solve this problem.