svga: Check if vertex elements has been bound before using it.

src/gallium/drivers/svga/svga_state_need_swtnl.c

@@ -76,6 +76,11 @@ static int update_need_swvfetch( struct svga_context *svga,
    unsigned i;
    boolean need_swvfetch = FALSE;
 
+   if (!svga->curr.velems) {
+      /* No vertex elements bound. */
+      return 0;
+   }
+
    for (i = 0; i < svga->curr.velems->count; i++) {
       svga->state.sw.ve_format[i] = svga_translate_vertex_format(svga->curr.velems->velem[i].src_format);
       if (svga->state.sw.ve_format[i] == SVGA3D_DECLTYPE_MAX) {