device: do not crash on nil'd bind in windows binding

device/boundif_windows.go

@@ -7,6 +7,7 @@ package device
 
 import (
 	"encoding/binary"
+	"errors"
 	"unsafe"
 
 	"golang.org/x/sys/windows"
@@ -23,6 +24,10 @@ func (device *Device) BindSocketToInterface4(interfaceIndex uint32) error {
 	binary.BigEndian.PutUint32(bytes, interfaceIndex)
 	interfaceIndex = *(*uint32)(unsafe.Pointer(&bytes[0]))
 
+	if device.net.bind == nil {
+		return errors.New("Bind is not yet initialized")
+	}
+
 	sysconn, err := device.net.bind.(*nativeBind).ipv4.SyscallConn()
 	if err != nil {
 		return err