[dns-client] allow empty question section in response with error code (#7438)
[dns-client] allow empty question section in response with error code (#7438)

This commit updates `Dns::Client` such that when parsing a query
response we allow and accept a message with empty question section if
the response code in header indicates an error. This ensures that the
`Dns::Client` can work with DNS name resolvers that may not echo back
the question section in case of an error response.
abtink/openthread,srickardti/openthread,abtink/openthread,openthread/openthread,jwhui/openthread,jwhui/openthread,openthread/openthread,openthread/openthread,abtink/openthread,abtink/openthread,srickardti/openthread,openthread/openthread,jwhui/openthread,srickardti/openthread,jwhui/openthread,srickardti/openthread