Sc-server failed if kb is empty

[NikitaZotov]

Describe the bug
If kb.bin directory doesn't exist or is empty sc-server will failed.

To Reproduce
Steps to reproduce the behavior:

1. Clear kb.bin folder
2. Not build kb
3. Run sc-server

Expected behavior
Run sc-server can work without any kb sources.

Desktop (please complete the following information):

• OS: [e.g. Ubuntu 20.04]
• Version [e.g. 0.6.1]