Reset neutral gray on start of new sequence

BUG=oss-fuzz:10061

Change-Id: I4ea0844a0441e0efcd2d00fc86169619e22c2369

av1/decoder/decodeframe.c

diff --git a/av1/decoder/decodeframe.c b/av1/decoder/decodeframe.c
index 9a1fb33..c7a4d94 100644
--- a/av1/decoder/decodeframe.c
+++ b/av1/decoder/decodeframe.c
@@ -4379,6 +4379,7 @@
 
 static INLINE void reset_frame_buffers(AV1_COMMON *cm) {
   RefCntBuffer *const frame_bufs = cm->buffer_pool->frame_bufs;
+  const SequenceHeader *const seq_params = &cm->seq_params;
   int i;
 
   memset(&cm->ref_frame_map, -1, sizeof(cm->ref_frame_map));
@@ -4392,6 +4393,9 @@
                                      &frame_bufs[i].raw_frame_buffer);
     }
     frame_bufs[i].cur_frame_offset = 0;
+    // Previous sequence with different bitdepth may have set to a
+    // neutral gray in different bit depth, need reset here.
+    set_planes_to_neutral_grey(seq_params, &frame_bufs[i].buf, 0);
     av1_zero(frame_bufs[i].ref_frame_offset);
   }
   unlock_buffer_pool(cm->buffer_pool);