[fix][client-cpp] Fix Reader segfault when messageListenerThreads=0 #1122

Job	Run time
Formatting Check	1m 41s
Lint	38m 10s
Build the Wireshark dissector (ubuntu-latest)	42s
Run unit tests	32m 51s
Build CPP Client on Windows x64	1h 1m 14s
Build CPP Client on Windows x86	56m 38s
Build CPP Client on macOS with static dependencies	9m 18s
Build with the C++20 standard	5m 42s
Build Alpine x86_64	30m 22s
Build Deb x86_64	19m 47s
Build RPM x86_64	19m 59s
Check Completion	2s
	4h 36m 26s

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