h264: Do not share rbsp_buffer across threads

Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

CC: libav-stable@libav.org
(cherry picked from commit 61928b68dc)
Signed-off-by: Anton Khirnov <anton@khirnov.net>

libavcodec/h264.c

@@ -686,6 +686,10 @@ static int decode_init_thread_copy(AVCodecContext *avctx)
     memset(h->sps_buffers, 0, sizeof(h->sps_buffers));
     memset(h->pps_buffers, 0, sizeof(h->pps_buffers));
 
+    h->rbsp_buffer[0]      = NULL;
+    h->rbsp_buffer[1]      = NULL;
+    h->rbsp_buffer_size[0] = 0;
+    h->rbsp_buffer_size[1] = 0;
     h->context_initialized = 0;
 
     return 0;