fix endpoint nil pointer

Author: Larvan2

stack_gvisor.go

@@ -153,7 +153,9 @@ func (t *GVisor) Start() error {
 }
 
 func (t *GVisor) Close() error {
-	t.endpoint.Attach(nil)
+	if t.endpoint != nil {
+		t.endpoint.Attach(nil)
+	}
 	t.stack.Close()
 	for _, endpoint := range t.stack.CleanupEndpoints() {
 		endpoint.Abort()

stack_mixed.go

@@ -261,7 +261,9 @@ func (m *Mixed) packetLoop() {
 }
 
 func (m *Mixed) Close() error {
-	m.endpoint.Attach(nil)
+	if m.endpoint != nil {
+		m.endpoint.Attach(nil)
+	}
 	m.stack.Close()
 	for _, endpoint := range m.stack.CleanupEndpoints() {
 		endpoint.Abort()