Checkmk Werk 10881: Fix possible crash when trying to save site multiple times

ID: 10881 Title: Fix possible crash when trying to save site multiple times Component: WATO Level: 1 Class: Bug fix Version: 1.7.0i1 When saving a site configuration and trying to submit the form again a second time, this could result in an error message. No information was lost, just the result of the page is not displayed correctly