draw: fix nonzero stream primitives generated queries

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>