Exclude zero vectors for cosine distance to be consistent with other types [skip ci]

sql/vector.sql

@@ -912,6 +912,7 @@ CREATE OPERATOR CLASS minivec_cosine_ops
 	FOR TYPE minivec USING ivfflat AS
 	OPERATOR 1 <=> (minivec, minivec) FOR ORDER BY float_ops,
 	FUNCTION 1 cosine_distance(minivec, minivec),
+	FUNCTION 2 l2_norm(minivec),
 	FUNCTION 3 minivec_spherical_distance(minivec, minivec),
 	FUNCTION 4 l2_norm(minivec),
 	FUNCTION 5 ivfflat_minivec_support(internal);