Checkmk Werk 14466: Fix ValueError on usage of empty service level filter

ID: 14466 Title: Fix ValueError on usage of empty service level filter Component: Multisite Level: 1 Class: Bug fix Version: 2.2.0i1 If "Host service level" or "Service service level" was used without "From" and "To" values in views, the error "ValueError: invalid literal for int() with base 10: ''" occurred.