Hysteria client: Remove closed instance conn (#7107)

https://github.com/XTLS/Xray-core/pull/7102#issuecomment-6054105250

Fixes https://github.com/XTLS/Xray-core/issues/7100

---------

Co-authored-by: LjhAUMEM <llnu14702@gmail.com>

core/xray.go

@@ -92,6 +92,8 @@ type Instance struct {
 
 // Instance state
 func (server *Instance) IsRunning() bool {
+	server.statusLock.Lock()
+	defer server.statusLock.Unlock()
 	return server.running
 }
 
@@ -320,7 +322,7 @@ func (s *Instance) RequireFeatures(callback interface{}, optional bool) error {
 
 // AddFeature registers a feature into current Instance.
 func (s *Instance) AddFeature(feature features.Feature) error {
-	if s.running {
+	if s.IsRunning() {
 		if err := feature.Start(); err != nil {
 			errors.LogInfoInner(s.ctx, err, "failed to start feature")
 		}