server(ticdc): fix panic issue if capture is not initialized (#9746)

close #9745

cdc/server/server.go

@@ -371,6 +371,11 @@ func (s *server) run(ctx context.Context) (err error) {
 // Drain removes tables in the current TiCDC instance.
 // It's part of graceful shutdown, should be called before Close.
 func (s *server) Drain() <-chan struct{} {
+	if s.capture == nil {
+		done := make(chan struct{})
+		close(done)
+		return done
+	}
 	return s.capture.Drain()
 }
 

pkg/cmd/server/server.go

@@ -131,8 +131,7 @@ func (o *options) run(cmd *cobra.Command) error {
 		return errors.Trace(err)
 	}
 	// Drain the server before shutdown.
-	shutdownNotify := func() <-chan struct{} { return server.Drain() }
-	util.InitSignalHandling(shutdownNotify, cancel)
+	util.InitSignalHandling(server.Drain, cancel)
 
 	// Run TiCDC server.
 	err = server.Run(ctx)