oggparsevorbis: use av_realloc consistently

Memory passed to av_realloc cannot be allocated using memalign.

From realloc(3):

The realloc() function changes the size of the memory block pointed to
by ptr to size bytes. (...) Unless ptr is NULL, it must have been returned
by an earlier call to malloc(), calloc() or realloc().

The issue has been found by debugallocation, a part of google-perftools:
http://code.google.com/p/gperftools/ .
Signed-off-by: Paweł Hajdan, Jr <phajdan@google.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/oggparsevorbis.c

@@ -173,11 +173,13 @@ static unsigned int
 fixup_vorbis_headers(AVFormatContext * as, struct oggvorbis_private *priv,
                      uint8_t **buf)
 {
-    int i,offset, len;
+    int i,offset, len, buf_len;
     unsigned char *ptr;
 
     len = priv->len[0] + priv->len[1] + priv->len[2];
-    ptr = *buf = av_mallocz(len + len/255 + 64);
+    buf_len = len + len/255 + 64;
+    ptr = *buf = av_realloc(NULL, buf_len);
+    memset(*buf, '\0', buf_len);
 
     ptr[0] = 2;
     offset = 1;