avformat/vividas: fix misaligned access

Fixes: ffmpeg_xor_block_libavformat_vividas.c_134_15.poc

Found-by: iceray-Li
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/vividas.c

@@ -131,7 +131,7 @@ static void xor_block(void *p1, void *p2, unsigned size, int key, unsigned *key_
     size >>= 2;
 
     while (size > 0) {
-        *d2 = *d1 ^ (HAVE_BIGENDIAN ? av_bswap32(k) : k);
+        AV_WN32(d2, AV_RN32(d1) ^ (HAVE_BIGENDIAN ? av_bswap32(k) : k));
         k += key;
         d1++;
         d2++;