The specifications for the Level 2 BLAS are given in:
J. J. Dongarra, J. Du Croz, S. Hammarling, and R. J. Hanson. An extended
set of FORTRAN Basic Linear Algebra Subprograms. ACM Trans. Math.
Software, 14:1?32, 399, 1988.
and on page 5 we have:
"Note that it is permissible to call the routines with M or N = 0, in
which case the routines exit immediately without referencing their
vector or matrix arguments."
so, although it might not be what you expect, the reference
implementation is behaving correctly.