[v4.1.x] pml/ucx: fix zero sized datatype transfers#8142

jsquyres merged 1 commit intoopen-mpi:v4.1.xopen-mpi/ompi:v4.1.xfrom

AboorvaDevarajan:fix_zero_byte_v4.1.xAboorvaDevarajan/ompi:fix_zero_byte_v4.1.xCopy head branch name to clipboard