### Environment

* Dubbo version: 2.7.2
* Operating System version: MacOS
* Java version: 1.8

### Steps to reproduce this issue
We have internal dubbo version 2.6.2.1 which bases dubbo-2.6.2。
1. Consumer side dubbo version is 2.6.2.1
2. Provider side dubbo version is 2.7.2
3. Invoke Exception

### Expected Result

Don't throw exception

### Actual Result
the exception trace:

```
Caused by: com.alibaba.dubbo.remoting.RemotingException: java.io.IOException: Unknown result flag, expect '0' '1' '2', get 4
java.io.IOException: Unknown result flag, expect '0' '1' '2', get 4
        at com.alibaba.dubbo.rpc.protocol.dubbo.DecodeableRpcResult.decode(DecodeableRpcResult.java:101)
        at com.alibaba.dubbo.rpc.protocol.dubbo.DecodeableRpcResult.decode(DecodeableRpcResult.java:113)
        at com.alibaba.dubbo.rpc.protocol.dubbo.DubboCodec.decodeBody(DubboCodec.java:89)
        at com.alibaba.dubbo.remoting.exchange.codec.ExchangeCodec.decode(ExchangeCodec.java:124)
        at com.alibaba.dubbo.remoting.exchange.codec.ExchangeCodec.decode(ExchangeCodec.java:84)
        at com.alibaba.dubbo.rpc.protocol.dubbo.DubboCountCodec.decode(DubboCountCodec.java:46)
        at com.alibaba.dubbo.remoting.transport.netty.NettyCodecAdapter$InternalDecoder.messageReceived(NettyCodecAdapter.java:133)
        at org.jboss.netty.channel.SimpleChannelUpstreamHandler.handleUpstream(SimpleChannelUpstreamHandler.java:70)
        at org.jboss.netty.channel.DefaultChannelPipeline.sendUpstream(DefaultChannelPipeline.java:564)
        at org.jboss.netty.channel.DefaultChannelPipeline.sendUpstream(DefaultChannelPipeline.java:559)
        at org.jboss.netty.channel.Channels.fireMessageReceived(Channels.java:268)
        at org.jboss.netty.channel.Channels.fireMessageReceived(Channels.java:255)
        at org.jboss.netty.channel.socket.nio.NioWorker.read(NioWorker.java:88)
        at org.jboss.netty.channel.socket.nio.AbstractNioWorker.process(AbstractNioWorker.java:109)
        at org.jboss.netty.channel.socket.nio.AbstractNioSelector.run(AbstractNioSelector.java:312)
        at org.jboss.netty.channel.socket.nio.AbstractNioWorker.run(AbstractNioWorker.java:90)
        at org.jboss.netty.channel.socket.nio.NioWorker.run(NioWorker.java:178)
        at org.jboss.netty.util.ThreadRenamingRunnable.run(ThreadRenamingRunnable.java:108)
        at org.jboss.netty.util.internal.DeadLockProofWorker$1.run(DeadLockProofWorker.java:42)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at java.lang.Thread.run(Thread.java:748)

        at com.alibaba.dubbo.remoting.exchange.support.DefaultFuture.returnFromResponse(DefaultFuture.java:222) ~[dubbo-2.6.2.1.jar:2.6.2.1]
        at com.alibaba.dubbo.remoting.exchange.support.DefaultFuture.get(DefaultFuture.java:139) ~[dubbo-2.6.2.1.jar:2.6.2.1]
        at com.alibaba.dubbo.remoting.exchange.support.DefaultFuture.get(DefaultFuture.java:112) ~[dubbo-2.6.2.1.jar:2.6.2.1]
        at com.alibaba.dubbo.rpc.protocol.dubbo.DubboInvoker.doInvoke(DubboInvoker.java:95) ~[dubbo-2.6.2.1.jar:2.6.2.1]
        at com.alibaba.dubbo.rpc.protocol.AbstractInvoker.invoke(AbstractInvoker.java:148) ~[dubbo-2.6.2.1.jar:2.6.2.1]
        at com.alibaba.dubbo.rpc.listener.ListenerInvokerWrapper.invoke(ListenerInvokerWrapper.java:77) ~[dubbo-2.6.2.1.jar:2.6.2.1]
        at com.alibaba.dubbo.rpc.protocol.ProtocolFilterWrapper$1.invoke(ProtocolFilterWrapper.java:72) ~[dubbo-2.6.2.1.jar:2.6.2.1]
        at com.alibaba.dubbo.rpc.protocol.ProtocolFilterWrapper$1.invoke(ProtocolFilterWrapper.java:72) ~[dubbo-2.6.2.1.jar:2.6.2.1]
        at com.alibaba.dubbo.monitor.support.MonitorFilter.invoke(MonitorFilter.java:75) ~[dubbo-2.6.2.1.jar:2.6.2.1]
        at com.alibaba.dubbo.rpc.protocol.ProtocolFilterWrapper$1.invoke(ProtocolFilterWrapper.java:72) ~[dubbo-2.6.2.1.jar:2.6.2.1]
        at com.alibaba.dubbo.rpc.protocol.dubbo.filter.FutureFilter.invoke(FutureFilter.java:54) ~[dubbo-2.6.2.1.jar:2.6.2.1]
        at com.alibaba.dubbo.rpc.protocol.ProtocolFilterWrapper$1.invoke(ProtocolFilterWrapper.java:72) ~[dubbo-2.6.2.1.jar:2.6.2.1]
        at com.alibaba.dubbo.rpc.protocol.ProtocolFilterWrapper$1.invoke(ProtocolFilterWrapper.java:72) ~[dubbo-2.6.2.1.jar:2.6.2.1]
        at com.alibaba.dubbo.rpc.protocol.ProtocolFilterWrapper$1.invoke(ProtocolFilterWrapper.java:72) ~[dubbo-2.6.2.1.jar:2.6.2.1]
        at com.alibaba.dubbo.rpc.filter.ConsumerContextFilter.invoke(ConsumerContextFilter.java:48) ~[dubbo-2.6.2.1.jar:2.6.2.1]
        at com.alibaba.dubbo.rpc.protocol.ProtocolFilterWrapper$1.invoke(ProtocolFilterWrapper.java:72) ~[dubbo-2.6.2.1.jar:2.6.2.1]
        at com.alibaba.dubbo.rpc.protocol.InvokerWrapper.invoke(InvokerWrapper.java:56) ~[dubbo-2.6.2.1.jar:2.6.2.1]
        at com.alibaba.dubbo.rpc.cluster.support.FailoverClusterInvoker.doInvoke(FailoverClusterInvoker.java:78) ~[dubbo-2.6.2.1.jar:2.6.2.1]
        ... 8 more

```
}
    public static boolean isSupportResponseAttachment(String version) {
        if (StringUtils.isEmpty(version)) {
            return false;
        }
        
        
        int iVersion = getIntVersion(version);
        if (iVersion >= 2001000 && iVersion <= 2060200) {
            return false;
        }
        
        if (iVersion >= 2080000 && iVersion < 2090000) {
            return false;
        }
        return iVersion >= LOWEST_VERSION_FOR_RESPONSE_ATTACHMENT;
    }
    public static int getIntVersion(String version) {
        Integer v = VERSION2INT.get(version);
        if (v == null) {
            v = parseInt(version);
            
            if (version.split("\\.").length == 3) {
                v = v * 100;
            }
            VERSION2INT.put(version, v);
        }
        return v;
    }
    private static int parseInt(String version) {