lib/model: Fixed adding empty items to device list (fixes #8646) (#8647)

lib/model/model.go

@@ -1278,7 +1278,7 @@ func (m *model) ClusterConfig(deviceID protocol.DeviceID, cm protocol.ClusterCon
 			for _, fcfg := range folders {
 				cfg.Folders = append(cfg.Folders, fcfg)
 			}
-			cfg.Devices = make([]config.DeviceConfiguration, len(devices))
+			cfg.Devices = make([]config.DeviceConfiguration, 0, len(devices))
 			for _, dcfg := range devices {
 				cfg.Devices = append(cfg.Devices, dcfg)
 			}