### 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

```
Assertions.assertTrue(Version.isSupportResponseAttachment("2.0.3"));
        Assertions.assertFalse(Version.isSupportResponseAttachment("2.0.0"));
    }
    @Test
    public void testGetIntVersion() {
        Assertions.assertEquals(2060100, Version.getIntVersion("2.6.1"));
        Assertions.assertEquals(2060101, Version.getIntVersion("2.6.1.1"));
        Assertions.assertEquals(2070001, Version.getIntVersion("2.7.0.1"));
        Assertions.assertEquals(2070000, Version.getIntVersion("2.7.0"));
    }
    @Test
    public void testIsFramework270OrHigher() {
        Assertions.assertTrue(Version.isRelease270OrHigher("2.7.0"));
        Assertions.assertTrue(Version.isRelease270OrHigher("2.7.0.1"));
        Assertions.assertTrue(Version.isRelease270OrHigher("2.7.0.2"));
        Assertions.assertTrue(Version.isRelease270OrHigher("2.8.0"));
        Assertions.assertFalse(Version.isRelease270OrHigher("2.6.3"));
        Assertions.assertFalse(Version.isRelease270OrHigher("2.6.3.1"));
    }
    @Test
    public void testIsFramework263OrHigher() {
        Assertions.assertTrue(Version.isRelease263OrHigher("2.7.0"));
        Assertions.assertTrue(Version.isRelease263OrHigher("2.7.0.1"));
        Assertions.assertTrue(Version.isRelease263OrHigher("2.6.4"));
        Assertions.assertFalse(Version.isRelease263OrHigher("2.6.2"));
        Assertions.assertFalse(Version.isRelease263OrHigher("2.6.1.1"));
        Assertions.assertTrue(Version.isRelease263OrHigher("2.6.3"));
    }
}