Checkmk Werk 12172: Fixed CMC crash after migration from Nagios

ID: 12172 Title: Fixed CMC crash after migration from Nagios Component: cmc Level: 1 Class: Bug fix Version: 2.1.0i1 When a site is migrated from using the Nagios core to using the CMC and there are already non-persistent acknowledgements, the CMC will crash during startup. This has been fixed, and those acknowledgements will still be there.