Merge PR #65656 into wip-vshankar-testing-20260324.125053

* refs/pull/65656/head:
	client: do not allow zero‑length reads
	src/test: test zero-length async-fsync read using ceph_ll_nonblocking_readv_writev
	src/test: test zero-length async-fsync read using ll_preadv_pwritev

Reviewed-by: Christopher Hoffman <choffman@redhat.com>

diff --cc src/client/Client.cc
Simple merge

diff --cc src/test/libcephfs/test.cc
Simple merge