Checkmk Werk 13245: Fix error on editing labels in rule conditions

ID: 13245 Title: Fix error on editing labels in rule conditions Component: Multisite Level: 1 Class: Bug fix Version: 2.1.0i1 If existing label conditions in rulesets were edited, e.g. "foo:bar" to "foo:baz", the error "Only one value per KEY can be used at a time.foo:baz is already used." occured.