Fix nullptr after listener consumer closed #967

Job	Run time
Formatting Check	1m 40s
Lint	27m 2s
Run unit tests	17m 54s
Build the Wireshark dissector (ubuntu-latest)	2m 3s
Build CPP Client on ${{ matrix.name }}	0s
Build ${{ matrix.pkg.name }} ${{ matrix.cpu.platform }}	1s
Build with the C++20 standard	1s
Build CPP Client on macOS with static dependencies	1s
Check Completion	1s
	48m 43s

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