Fix nullptr after listener consumer closed

[shibd]

Fix failed Node.js client test cpp 3.8.0 CI: https://github.com/apache/pulsar-client-node/actions/runs/18549226483/job/52888496279?pr=437

Motivation

Fix a segmentation fault when the consumer is closed.

* thread #6, stop reason = EXC_BAD_ACCESS (code=1, address=0x13c)
  * frame #0: 0x0000000102cae94c pulsar-tests`pulsar::SharedBuffer::readableBytes(this=0x0000000000000120) const at SharedBuffer.h:146:52
    frame #1: 0x0000000103212ce0 pulsar-tests`pulsar::Message::getLength(this=0x000000016d5f2670) const at Message.cc:57:64
    frame #2: 0x0000000103238410 pulsar-tests`pulsar::MultiTopicsConsumerImpl::messageProcessed(this=0x000000013800ba18, msg=0x000000016d5f2670) at MultiTopicsConsumerImpl.cc:1110:41
    frame #3: 0x0000000103238198 pulsar-tests`pulsar::MultiTopicsConsumerImpl::internalListener(this=0x000000013800ba18, consumer=0x00006000000c8668) at MultiTopicsConsumerImpl.cc:561:9
    frame #4: 0x0000000103256b2c pulsar-tests`decltype(*std::declval<std::__1::shared_ptr<pulsar::MultiTopicsConsumerImpl>&>().*std::declval<void (pulsar::MultiTopicsConsumerImpl::*&)(pulsar::Consumer const&)>()(std::declval<pulsar::Consumer&>())) std::__1::__invoke[abi:ne190102]<void (pulsar::MultiTopicsConsumerImpl::*&)(pulsar::Consumer const&), std::__1::shared_ptr<pulsar::MultiTopicsConsumerImpl>&, pulsar::Consumer&, void>(__f=0x00006000000c8648, __a0=std::__1::shared_ptr<pulsar::MultiTopicsConsumerImpl>::element_type @ 0x000000013800ba18 strong=9 weak=16, __args=0x00006000000c8668) at invoke.h:117:25

Root cause:

1. When the consumer is closed, incomingMessages_ queue is closed.
2. However, if there are in-flight messages before closing, they will be processed in the internalListener method, which attempts to pop message content from the incomingMessages_ queue.
3. The closed incomingMessages_ will return null, leading to a segmentation fault when accessing the message.

Modifications

1. Check if the message popping from incomingMessages_ false (indicating no more messages or queue closed). If so, return early.

Verifying this change

• The testConsumerListenerShouldNotSegfaultAfterClose test can be used to reproduce and verify the fix for this issue.

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[BewareMyPower]

Pulsar/ReaderTest.testHasMessageAvailableWhenCreated/0 also failed for master branch, not sure why it happened, I will take a look at this issue.