policy.FLAGS: fix not applying properly in edge cases

Perhaps this bug was now more pronounced since 5.3.0 changes. Example problem was disabling minimization or 0x20 (globally or for some problematic requests); without this change they would get re-enabled during some fallback actions... which might be exactly the wrong moment wrt. the motivation to setting these. https://gitter.im/CZ-NIC/knot-resolver?at=60a221e86a950f3d46ed1cd9