Fix MSAN error in rdtime.h

[fdr400]

trafficstars

Resolves #4865

[confluent-cla-assistant[bot]]

:tada: All Contributor License Agreements have been signed. Ready to merge.
:white_check_mark: fdr400
_{Please push an empty commit if you would like to re-run the checks to verify CLA status for all contributors.}

[cla-assistant[bot]]

All committers have signed the CLA.

[fdr400]

@emasab Hello! Can you review the changes, please. We already imported the patch into our codebase and it MSAN tests start working

[fdr400]

@emasab