fix bug: 'http: multiple response.WriteHeader calls'
fix bug: 'http: multiple response.WriteHeader calls'

chrislusf/seaweedfs,chrislusf/seaweedfs,hxiaodon/seaweedfs,k85169336/seaweedfs,chrislusf/seaweedfs,k85169336/seaweedfs,chrislusf/seaweedfs,hxiaodon/seaweedfs