Fix nil pointer issue after restart of pod

[CodeClinch]

Description

After karydia is restarted the network policy reconciler will lead to a nil pointer exception. This PR will make better checks and reloads the network policies if necessary.

Checklist

Before submitting this PR, please make sure:

• [ ] you have added unit tests
• [ ] you have added integration tests
• [x] your code builds clean with make
• [x] your code lets succeed unit tests with make test
• [x] your code lets succeed integration tests
• [ ] you have documented new or changed features