Use av_mallocz() to initialize hwaccel_data_private.

Originally committed as revision 17942 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/avcodec.h

@@ -2467,9 +2467,9 @@ typedef struct AVHWAccel {
     /**
      * Size of HW accelerator private data.
      *
-     * Private data is allocated with av_malloc() before
-     * AVCodecContext::get_buffer() and deallocated after
-     * AVCodecContext::release_buffer().
+     * Private data is allocated with av_mallocz() before
+     * AVCodecContext.get_buffer() and deallocated after
+     * AVCodecContext.release_buffer().
      */
     int priv_data_size;
 } AVHWAccel;

libavcodec/mpegvideo.c

@@ -183,7 +183,7 @@ static int alloc_frame_buffer(MpegEncContext *s, Picture *pic)
     if (s->avctx->hwaccel) {
         assert(!pic->hwaccel_data_private);
         if (s->avctx->hwaccel->priv_data_size) {
-            pic->hwaccel_data_private = av_malloc(s->avctx->hwaccel->priv_data_size);
+            pic->hwaccel_data_private = av_mallocz(s->avctx->hwaccel->priv_data_size);
             if (!pic->hwaccel_data_private) {
                 av_log(s->avctx, AV_LOG_ERROR, "alloc_frame_buffer() failed (hwaccel private data allocation)\n");
                 return -1;