Fix topic lookup segmentation fault after client is closed #985

Job	Run time
Formatting Check	1m 37s
Run unit tests	2m 55s
Build the Wireshark dissector (ubuntu-latest)	2m 21s
Lint	2m 55s
Build CPP Client on ${{ matrix.name }}	1s
Build with the C++20 standard	1s
Build CPP Client on macOS with static dependencies	1s
Build ${{ matrix.pkg.name }} ${{ matrix.cpu.platform }}	1s
Check Completion	1s
	9m 53s

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