Workaround for hanging events. Fixes #4804

Docker-DCO-1.1-Signed-off-by: LK4D4 <lk4d4math@gmail.com> (github: LK4D4)

server/server.go

@@ -222,6 +222,10 @@ func (srv *Server) Events(job *engine.Job) engine.Status {
 
 	listener := make(chan utils.JSONMessage)
 	srv.Lock()
+	if old, ok := srv.listeners[from]; ok {
+		delete(srv.listeners, from)
+		close(old)
+	}
 	srv.listeners[from] = listener
 	srv.Unlock()
 	job.Stdout.Write(nil) // flush