st/mesa: avoid vertex texture and sampler updates for 0 case

If we had no vertex textures or samplers previously and we have none now,
don't bother doing the enables dance.

I was profiling nexuiz on noop and noticed these two functions in the
profile, this drops their usage from 0.86% to 0.03% and 0.23% to 0.03%
for texture and samplers.

Signed-off-by: Dave Airlie <airlied@redhat.com>

src/mesa/state_tracker/st_atom_sampler.c

@@ -201,6 +201,8 @@ update_vertex_samplers(struct st_context *st)
    struct gl_vertex_program *vprog = ctx->VertexProgram._Current;
    GLuint su;
 
+   if (st->state.num_vertex_samplers == 0 && vprog->Base.SamplersUsed == 0)
+       return;
    st->state.num_vertex_samplers = 0;
 
    /* loop over sampler units (aka tex image units) */

src/mesa/state_tracker/st_atom_texture.c

@@ -260,6 +260,9 @@ update_vertex_textures(struct st_context *st)
    struct gl_vertex_program *vprog = ctx->VertexProgram._Current;
    GLuint su;
 
+   if (!vprog->Base.SamplersUsed && st->state.num_vertex_textures == 0)
+      return;
+
    st->state.num_vertex_textures = 0;
 
    /* loop over sampler units (aka tex image units) */