mesa: only call update_buffer when it's available

diff --git a/src/mesa/state_tracker/st_cb_viewport.c b/src/mesa/state_tracker/st_cb_viewport.c
index 6adf3162c1e86ec6974b354b087be0b379c99990..7b175288fcb3061772da6edfcf203241ad88461f 100644 (file)
--- a/src/mesa/state_tracker/st_cb_viewport.c
+++ b/src/mesa/state_tracker/st_cb_viewport.c
@@ -40,7 +40,7 @@ static void st_viewport(GLcontext * ctx, GLint x, GLint y,
 {
    struct st_context *st = ctx->st;
 
-   if (st->pipe->winsys)
+   if (st->pipe->winsys && st->pipe->winsys->update_buffer)
       st->pipe->winsys->update_buffer( st->pipe->winsys,
                                        st->pipe->priv );
 }