Fix crash caused by Message::getTopicName when the message is a producer message #950

Job	Run time
Formatting Check	1m 43s
Lint	28m 25s
Build the Wireshark dissector (ubuntu-latest)	2m 7s
Run unit tests	18m 1s
Build CPP Client on Windows x64	35m 35s
Build CPP Client on Windows x86	31m 39s
Build with the C++20 standard	5m 44s
Build CPP Client on macOS with static dependencies	7m 29s
Build Deb x86_64	11m 51s
Build RPM x86_64	13m 0s
Build Alpine x86_64	11m 46s
Check Completion	1m 40s
	2h 49m 0s

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