libvpx: Pull from upstream

source/libvpx/vp9/encoder/vp9_mbgraph.c

 /*
  *  Copyright (c) 2010 The WebM project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 358 matching lines @@
 
   // Free localy allocated storage
   vpx_free(arf_not_zz);
 }
 
 void vp9_update_mbgraph_stats(VP9_COMP *cpi) {
   VP9_COMMON *const cm = &cpi->common;
   int i, n_frames = vp9_lookahead_depth(cpi->lookahead);
   YV12_BUFFER_CONFIG *golden_ref = get_ref_frame_buffer(cpi, GOLDEN_FRAME);
 
+  assert(golden_ref != NULL);
+
   // we need to look ahead beyond where the ARF transitions into
   // being a GF - so exit if we don't look ahead beyond that
   if (n_frames <= cpi->rc.frames_till_gf_update_due)
     return;
 
   if (n_frames > MAX_LAG_BUFFERS)
     n_frames = MAX_LAG_BUFFERS;
 
   cpi->mbgraph_n_frames = n_frames;
   for (i = 0; i < n_frames; i++) {
@@ skipping 14 matching lines @@
     assert(q_cur != NULL);
 
     update_mbgraph_frame_stats(cpi, frame_stats, &q_cur->img,
                                golden_ref, cpi->Source);
   }
 
   vp9_clear_system_state();
 
   separate_arf_mbs(cpi);
 }