all: Propagate errors from NamespacedKV (#6203)

As foretold by the prophecy, "once the database refactor is merged, then
shall appear a request to propagate errors from the store known
throughout the land as the NamedspacedKV, and it shall be good".

lib/model/model_test.go

@@ -3392,7 +3392,10 @@ func TestDeviceWasSeen(t *testing.T) {
 
 	m.deviceWasSeen(device1)
 
-	stats := m.DeviceStatistics()
+	stats, err := m.DeviceStatistics()
+	if err != nil {
+		t.Error("Unexpected error:", err)
+	}
 	entry := stats[device1.String()]
 	if time.Since(entry.LastSeen) > time.Second {
 		t.Error("device should have been seen now")