bug: PostRequest.getUpstreamHeaders cause IndexOutOfBoundsException Error

[lita-hufeng]

Issue description

When call request.getUpstreamHeaders() in postFilter, sometimes may cause IndexOutOfBoundsException.

Environment

apisix 3.9.0
apisix-java-plugin-runner 0.6.0

Minimal test code / Steps to reproduce the issue

Not every time it happens, there is about 4 times happens of 10 .

java.lang.IndexOutOfBoundsException: null
        at java.base/java.nio.Buffer$1.apply(Buffer.java:757) ~[na:na]
        at java.base/java.nio.Buffer$1.apply(Buffer.java:754) ~[na:na]
        at java.base/jdk.internal.util.Preconditions$4.apply(Preconditions.java:213) ~[na:na]
        at java.base/jdk.internal.util.Preconditions$4.apply(Preconditions.java:210) ~[na:na]
        at java.base/jdk.internal.util.Preconditions.outOfBounds(Preconditions.java:98) ~[na:na]
        at java.base/jdk.internal.util.Preconditions.outOfBoundsCheckIndex(Preconditions.java:106) ~[na:na]
        at java.base/jdk.internal.util.Preconditions.checkIndex(Preconditions.java:302) ~[na:na]
        at java.base/java.nio.Buffer.checkIndex(Buffer.java:779) ~[na:na]
        at java.base/java.nio.DirectByteBuffer.getInt(DirectByteBuffer.java:761) ~[na:na]
        at com.google.flatbuffers.Table.__vector_len(Table.java:125) ~[flatbuffers-java-2.0.0.jar!/:na]
        at io.github.api7.A6.HTTPRespCall.Req.headersLength(Req.java:22) ~[A6-0.6.0-RELEASE.jar!/:na]
        at org.apache.apisix.plugin.runner.PostRequest.getUpstreamHeaders(PostRequest.java:82) ~[apisix-runner-plugin-sdk-0.6.0.jar!/:0.6.0]
        at gg.lita.arch.gateway.plugin.filters.LitaLoginResponseFilter.getPostRequestHeaders(LitaLoginResponseFilter.java:52) ~[!/:0.0.1]

also PluginFilter implements is

    @Override
    public Boolean requiredBody() {
        return false;
    }

    @Override
    public Boolean requiredRespBody(){
        return true;
    }

What's the actual result? (including assertion message & call stack if applicable)

What's the expected result?

expect request.getUpstreamHeaders() can return normally.