FIX: NPE when thrift field is nested

[xuanyu66]

Fix

• Add a unit test to verify that the fix works.
• Explain briefly why the bug exists and how to fix it.

When thrift message has nested field, ServerInProtocolWrapper read Inner fieldStop and make context = null, then ServerInProtocolWrapper read outer fieldStop, which cause NPE.
So I move this logic to readMessageEnd() so that make sure it's invoked only once

ServerInProtocolWrapper#readFieldBegin()
    @Override
    public TField readFieldBegin() throws TException {
       ................
        if (field.type == TType.STOP) {
            Boolean haveCreatedSpan =
                    (Boolean) ContextManager.getRuntimeContext().get(HAVE_CREATED_SPAN);
            if (haveCreatedSpan != null && !haveCreatedSpan) {
                try {
                    AbstractSpan span = ContextManager.createEntrySpan(
                            context.getOperatorName(), createContextCarrier(null));
                    span.start(context.startTime);
                    span.tag(TAG_ARGS, context.getArguments());
                    span.setComponent(ComponentsDefine.THRIFT_SERVER);
                    SpanLayer.asRPCFramework(span);
                } catch (Throwable throwable) {
                    LOGGER.error("Failed to create EntrySpan.", throwable);
                } finally {
                    context = null;
                }

        return field;
    }

• If this pull request closes/resolves/fixes an existing issue, replace the issue number. Closes #.
• Update the CHANGES log.

[codecov]

Codecov Report

Merging #6909 (a5fcb54) into master (49d36cb) will decrease coverage by 14.38%.
The diff coverage is 5.71%.

❗ Current head a5fcb54 differs from pull request most recent head aa17b89. Consider uploading reports for the commit aa17b89 to get more accurate results

@@              Coverage Diff              @@
##             master    #6909       +/-   ##
=============================================
- Coverage     54.40%   40.01%   -14.39%     
+ Complexity     4227     2440     -1787     
=============================================
  Files          1844      824     -1020     
  Lines         39358    20674    -18684     
  Branches       4360     1976     -2384     
=============================================
- Hits          21411     8272    -13139     
+ Misses        16919    11740     -5179     
+ Partials       1028      662      -366     

Impacted Files	Coverage Δ	Complexity Δ
...er/receiver/envoy/EnvoyMetricReceiverProvider.java	73.33% <0.00%> (-14.67%)	8.00 <1.00> (ø)
...alking/oap/server/receiver/envoy/TCPOALDefine.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
...server/receiver/envoy/als/AbstractALSAnalyzer.java	0.00% <ø> (-50.00%)	0.00 <0.00> (ø)
...p/server/receiver/envoy/als/AccessLogAnalyzer.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
...er/receiver/envoy/als/LogEntry2MetricsAdapter.java	0.00% <ø> (-49.10%)	0.00 <0.00> (ø)
...ver/receiver/envoy/als/k8s/K8SServiceRegistry.java	0.00% <0.00%> (-0.81%)	0.00 <0.00> (ø)
...er/envoy/als/tcp/AbstractTCPAccessLogAnalyzer.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
...iver/envoy/als/tcp/TCPLogEntry2MetricsAdapter.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
...nvoy/als/tcp/k8s/K8sALSServiceMeshTCPAnalysis.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
...y/als/tcp/mx/MetaExchangeTCPAccessLogAnalyzer.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
... and 1490 more

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[dmsolr]

LGTM