gallium/u_vbuf: skip draws with 0 vertices

Reviewed-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8298>

src/gallium/auxiliary/util/u_vbuf.c

@@ -1487,11 +1487,14 @@ void u_vbuf_draw_vbo(struct u_vbuf *mgr, const struct pipe_draw_info *info,
          new_draw.count = end_vertex - new_draw.start;
          new_info.instance_count = end_instance - new_info.start_instance;
 
-         if (new_draw.start == ~0u || !new_draw.count || !new_info.instance_count)
+         if (new_draw.start == ~0u)
             goto cleanup;
       }
    }
 
+   if (!new_draw.count || !new_info.instance_count)
+      goto cleanup;
+
    if (new_info.index_size) {
       /* See if anything needs to be done for per-vertex attribs. */
       if (u_vbuf_need_minmax_index(mgr)) {