request help: I want to check in ext-plugin-post-resp plugin according to upstream response status.

### Issue description
When the upstream response status is 400 or 500, the postfilter cannot check the status.

my post filter is
```
@Override
public void postFilter(PostRequest request, PostResponse response, PluginFilterChain chain) {
log.info("--------------------post filter start------------11111111");
log.info(request.getUpstreamHeaders().toString());
log.info(request.getUpstreamStatusCode().toString());
log.info(request.getBody());
chain.postFilter(request, response);
}
```

When the upstream responds with 200, the log is
```
--------------------post filter start------------11111111
{Keep-Alive=timeout=60, Transfer-Encoding=chunked, test=1234, Connection=keep-alive, Date=Fri, 14 Jul 2023 02:12:15 GMT, Content-Type=application/json}
200
{"createdDate":null,"modifiedDate":null,"id":null,"name":"ccs","apiCode":"abcd"}
```

but, 400 or 500
```
--------------------post filter start------------11111111
{}
0
{"createdDate":null,"modifiedDate":null,"id":null,"name":"ccs","apiCode":"abcd"}
```
I want to process logic based on the upstream response status(200, 400, 500)
**can u check this problems?**
@nic-chen

and one more thing..
In about half of all calls, postfilter throws java.lang.IndexOutOfBoundsException: null.
error.log is
```
2023/07/14 11:35:23 [warn] 6638#6638: *17534332 [lua] init.lua:953: 2023-07-14 11:35:23.257 INFO 6652 --- [tLoopGroup-34-5] c.d.p.F.TestFilter : --------------------post filter start------------11111111
, context: ngx.timer
2023/07/14 11:35:23 [warn] 6638#6638: *17534332 [lua] init.lua:953: 2023-07-14 11:35:23.257 ERROR 6652 --- [tLoopGroup-34-5] o.a.a.p.r.h.RpcCallHandler : handle request error:

java.lang.IndexOutOfBoundsException: null
at java.nio.Buffer.checkIndex(Buffer.java:693) ~[?:?]
at java.nio.DirectByteBuffer.getInt(DirectByteBuffer.java:758) ~[?:?]
at com.google.flatbuffers.Table.__vector_len(Table.java:125) ~[flatbuffers-java-2.0.0.jar!/:?]
at io.github.api7.A6.HTTPRespCall.Req.headersLength(Req.java:22) ~[A6-0.6.0-RELEASE.jar!/:?]
at org.apache.apisix.plugin.runner.PostRequest.getUpstreamHeaders(PostRequest.java:81) ~[apisix-runner-plugin-sdk-0.4.0.jar!/:0.4.0]
at com.platform.Filter.TestFilter.postFilter(TestFilter.java:127) ~[classes!/:1.0.0]
at org.apache.apisix.plugin.runner.filter.PluginFilterChain.postFilter(PluginFilterChain.java:64) ~[apisix-runner-plugin-sdk-0.4.0.jar!/:0.4.0]
at org.apache.apisix.plugin.runner.handler.RpcCallHandler.doPostFilter(RpcCallHandler.java:211) ~[apisix-runner-core-0.4.0.jar!/:0.4.0]
at org.apache.apisix.plugin.runner.handler.RpcCallHandler.handleExtraInfo(RpcCallHandler.java:243) ~[apisix-runner-core-0.4.0.jar!/:0.4.0]
at org.apache.apisix.plugin.runner.handler.RpcCallHandler.channelRead0(RpcCallHandler.java:92) ~[apisix-runner-core-0.4.0.jar!/:0.4.0]
at org.apache.apisix.plugin.runner.handler.RpcCallHandler.channelRead0(RpcCallHandler.java:54) ~[apisix-runner-core-0.4.0.jar!/:0.4.0]
at io.netty.channel.SimpleChannelInboundHandler.channelRead(SimpleChannelInboundHandler.java:99) ~[netty-transport-4.1.78.Final.jar!/:4.1.78.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-transport-4.1.78.Final.jar!/:4.1.78.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-transport-4.1.78.Final.jar!/:4.1.78.Final]
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) ~[netty-transport-4.1.78.Final.jar!/:4.1.78.Final]
at org.apache.apisix.plugin.runner.handler.PrepareConfHandler.channelRead0(PrepareConfHandler.java:57) ~[apisix-runner-core-0.4.0.jar!/:0.4.0]
at org.apache.apisix.plugin.runner.handler.PrepareConfHandler.channelRead0(PrepareConfHandler.java:45) ~[apisix-runner-core-0.4.0.jar!/:0.4.0]
at io.netty.channel.SimpleChannelInboundHandler.channelRead(SimpleChannelInboundHandler.java:99) ~[netty-transport-4.1.78.Final.jar!/:4.1.78.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-transport-4.1.78.Final.jar!/:4.1.78.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-transport-4.1.78.Final.jar!/:4.1.78.Final]
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) ~[netty-transport-4.1.78.Final.jar!/:4.1.78.Final]
at org.apache.apisix.plugin.runner.handler.PayloadDecoder.channelRead0(PayloadDecoder.java:45) ~[apisix-runner-core-0.4.0.jar!/:0.4.0]
at org.apache.apisix.plugin.runner.handler.PayloadDecoder.channelRead0(PayloadDecoder.java:38) ~[apisix-runner-core-0.4.0.jar!/:0.4.0]
at io.netty.channel.SimpleChannelInboundHandler.channelRead(SimpleChannelInboundHandler.java:99) ~[netty-transport-4.1.78.Final.jar!/:4.1.78.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-transport-4.1.78.Final.jar!/:4.1.78.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-transport-4.1.78.Final.jar!/:4.1.78.Final]
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) ~[nett, context: ngx.timer
2023/07/14 11:35:23 [warn] 6638#6638: *17534332 [lua] init.lua:953: y-transport-4.1.78.Final.jar!/:4.1.78.Final]
at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:327) ~[netty-codec-4.1.78.Final.jar!/:4.1.78.Final]
at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:299) ~[netty-codec-4.1., context: ngx.timer
2023/07/14 11:35:23 [warn] 6638#6638: *17534332 [lua] init.lua:953: 78.Final.jar!/:4.1.78.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-transport-4.1.78.Final.jar!/:4.1.78.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-transport-4.1.78.Final.jar!/:4.1.78.Final]
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) ~[netty-transport-4.1.78.Final.jar!/:4.1.78.Final]
at io.netty.handler.logging.LoggingHandler.channelRead(LoggingHandler.java:280) ~[netty-handler-4.1.78.Final.jar!/:4.1.78.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-transport-4.1.78.Final.jar!/:4.1.78.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-transport-4.1.78.Final.jar!/:4.1.78.Final]
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) ~[netty-transport-4.1.78.Final.jar!/:4.1.78.Final]
at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1410) ~[netty-transport-4.1.78.Final.jar!/:4.1.78.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-transport-4.1.78.Final.jar!/:4.1.78.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-transport-4.1.78.Final.jar!/:4.1.78.Final]
at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:919) ~[netty-transport-4.1.78.Final.jar!/:4.1.78.Final]
at io.netty.channel.epoll.AbstractEpollStreamChannel$EpollStreamUnsafe.epollInReady(AbstractEpollStreamChannel.java:800) ~[netty-transport-classes-epoll-4.1.78.Final.jar!/:4.1.78.Final]
at io.netty.channel.epoll.EpollDomainSocketChannel$EpollDomainUnsafe.epollInReady(EpollDomainSocketChannel.java:138) ~[netty-transport-classes-epoll-4.1.78.Final.jar!/:4.1.78.Final]
at io.netty.channel.epoll.EpollEventLoop.processReady(EpollEventLoop.java:487) ~[netty-transport-classes-epoll-4.1.78.Final.jar!/:4.1.78.Final]
at io.netty.channel.epoll.EpollEventLoop.run(EpollEventLoop.java:385) ~[netty-transport-classes-epoll-4.1.78.Final.jar!/:4.1.78.Final]
at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:997) ~[netty-common-4.1.78.Final.jar!/:4.1.78.Final]
at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74) ~[netty-common-4.1.78.Final.jar!/:4.1.78.Final]
at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30) ~[netty-common-4.1.78.Final.jar!/:4.1.78.Final]
at java.lang.Thread.run(Thread.java:829) ~[?:?]
```
TestFilter.java:127 line is **'log.info(request.getUpstreamHeaders().toString())'**

thx in advance

### Environment
apisix 3.2.0, 3.2.1
apisix-java-plugin-runner 0.4.0