libvpx: Pull from upstream

source/libvpx/vp9/decoder/vp9_decodeframe.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 1059 matching lines @@
   cm->profile = read_profile(rb);
   if (cm->profile >= MAX_PROFILES)
     vpx_internal_error(&cm->error, VPX_CODEC_UNSUP_BITSTREAM,
                        "Unsupported bitstream profile");
 
   cm->show_existing_frame = vp9_rb_read_bit(rb);
   if (cm->show_existing_frame) {
     // Show an existing frame directly.
     const int frame_to_show = cm->ref_frame_map[vp9_rb_read_literal(rb, 3)];
 
-    if (cm->frame_bufs[frame_to_show].ref_count < 1)
+    if (frame_to_show < 0 || cm->frame_bufs[frame_to_show].ref_count < 1)
       vpx_internal_error(&cm->error, VPX_CODEC_UNSUP_BITSTREAM,
                          "Buffer %d does not contain a decoded frame",
                          frame_to_show);
 
     ref_cnt_fb(cm->frame_bufs, &cm->new_fb_idx, frame_to_show);
     pbi->refresh_frame_flags = 0;
     cm->lf.filter_level = 0;
     cm->show_frame = 1;
     return 0;
   }
@@ skipping 291 matching lines @@
         vp9_adapt_mv_probs(cm, cm->allow_high_precision_mv);
       }
     } else {
       debug_check_frame_counts(cm);
     }
   }
 
   if (cm->refresh_frame_context)
     cm->frame_contexts[cm->frame_context_idx] = cm->fc;
 }