avidec: zero extradata padding

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/avidec.c

@@ -704,7 +704,7 @@ static int avi_read_header(AVFormatContext *s)
 
                 if(size<(1<<30)){
                     st->codec->extradata_size= size;
-                    st->codec->extradata= av_malloc(st->codec->extradata_size + FF_INPUT_BUFFER_PADDING_SIZE);
+                    st->codec->extradata= av_mallocz(st->codec->extradata_size + FF_INPUT_BUFFER_PADDING_SIZE);
                     if (!st->codec->extradata) {
                         st->codec->extradata_size= 0;
                         return AVERROR(ENOMEM);