Merge pull request #309 from thaJeztah/19.03_backport_prevent_network_attach_panic

[19.03 backport] Prevent panic on network attach

daemon/container_operations.go

@@ -237,7 +237,10 @@ func (daemon *Daemon) buildSandboxOptions(container *container.Container) ([]lib
 
 func (daemon *Daemon) updateNetworkSettings(container *container.Container, n libnetwork.Network, endpointConfig *networktypes.EndpointSettings) error {
 	if container.NetworkSettings == nil {
-		container.NetworkSettings = &network.Settings{Networks: make(map[string]*network.EndpointSettings)}
+		container.NetworkSettings = &network.Settings{}
+	}
+	if container.NetworkSettings.Networks == nil {
+		container.NetworkSettings.Networks = make(map[string]*network.EndpointSettings)
 	}
 
 	if !container.HostConfig.NetworkMode.IsHost() && containertypes.NetworkMode(n.Type()).IsHost() {