graphing/designer: block a query without a host and a service filter

A filter counts only when it holds a value, so one that was just picked still
blocks. Telling the two apart needs the API's filter definitions, bound by
useItemValidation where a row's completeness is asked for.

Change-Id: Ia0a26ff2c945ca92bd064ba27d2b2ced15667fb3
JIRA-Ref: CMK-38111