msg/async/rdma: fix a coredump introduced by PR #18053, #18204
The following tests FAILED:
AFAICT, pulpito is not triggered by any label on github.
some kind developer will collect the "needs-qa" PRs for testing them in batch, and analyze the test result, then hopefully merge the tested PRs if all goes well. and it does not happen automatically. normally, this takes up to one week.