Removal of stack fails if log group do not exists

[fogfish]

Removal of custom c3.LogGroup resources fails if log group is removed manually (outside of CF process).

Error message in logs

{
    "Status": "FAILED",
    ...
    "Data": {
        "reason": {
            "message": "The specified log group does not exist.",
            "code": "ResourceNotFoundException",
            ...
        }
    }
}