Werk #951: table servicegroups: fixed service visibility when using group_authorization AUTH_STRICT

This only applies with the setting group_authorization = AUTH_STRICT

When an auth user was given the livestatus table servicegroups did not check if the auth user had permissions to all objects of the servicegroup. As a result the user was able to view servicegroups, even if he was not a contact for every object in it. However, the "forbidden" object itself was not returned, just a subset of the group. This was incorrect. The user needs to be contact of every element in this group. Otherwise he should not see the group at all..

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