draw: fix nonzero stream primitives generated queries
the fastpath here can only be taken if there is exactly one stream active,
as this will otherwise break nonzero stream primitives generated queries
in truth, this num_vertex_streams thing should be a bitmask so that the case
of num_streams=1,stream_id!=0 could also be fastpathed, but the complexity
probably isn't worth it given the infrequency of use
cc: mesa-stable
Reviewed-by: Dave Airlie <airlied@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15506>