Judge a send on no machine as the core, and test a send carrying the core with the real classes

The review found that a send whose first machine runs none of its
modules would pass at once with no reading, and that every mixed send
in the tests judged its leaf as the core.

cmd/mesh-controller/gate_test.go

@@ -300,6 +300,7 @@ func TestAModuleIsJudgedByItsClass(t *testing.T) {
 		{"mesh-host", nil, 3, true},
 		{"node-tools", nil, 3, true},
 		{"nats", nil, 3, true},
+		{catalogue.DeliverySeat, nil, 3, true},
 		{"dnsmasq", []catalogue.Claim{{Name: resolverSeat}}, 3, true},
 	} {
 		p, s := gateWants(c.module, catalogue.Manifest{Module: c.module, Claims: c.claims})