Mesa (master): softpipe: fix crash when accessing null colorbuffer

[Brian Paul]

Module: Mesa
Branch: master
Commit: 3ede8dd5f1096531a080bac6f17f2512bea7bbce
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=3ede8dd5f1096531a080bac6f17f2512bea7bbce

Author: Brian Paul <brianp at vmware.com>
Date:   Mon Jan 20 07:59:25 2014 -0800

softpipe: fix crash when accessing null colorbuffer

Fixes piglit fbo-missing-attachment-blit test.
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=73755

Reviewed-by: Roland Scheidegger <sroland at vmware.com>

---

 src/gallium/drivers/softpipe/sp_quad_blend.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/gallium/drivers/softpipe/sp_quad_blend.c b/src/gallium/drivers/softpipe/sp_quad_blend.c
index fb19ba5..41149a0 100644
--- a/src/gallium/drivers/softpipe/sp_quad_blend.c
+++ b/src/gallium/drivers/softpipe/sp_quad_blend.c
@@ -1232,7 +1232,10 @@ choose_blend_quad(struct quad_stage *qs,
             softpipe->blend->rt[0].colormask == 0xf &&
             softpipe->framebuffer.nr_cbufs == 1)
    {
-      if (!blend->rt[0].blend_enable) {
+      if (softpipe->framebuffer.cbufs[0] == NULL) {
+         qs->run = blend_noop;
+      }
+      else if (!blend->rt[0].blend_enable) {
          qs->run = single_output_color;
       }
       else if (blend->rt[0].rgb_src_factor == blend->rt[0].alpha_src_factor &&