Fix uninitialized reads for fate-vsynth1-asv2 test.

This is not a real error and memsetting always even when the
size did not change is overkill, but it still should be
an acceptable trade-off.
Signed-off-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>

libavcodec/asv1.c

@@ -411,6 +411,7 @@ static int decode_frame(AVCodecContext *avctx,
     av_fast_malloc(&a->bitstream_buffer, &a->bitstream_buffer_size, buf_size + FF_INPUT_BUFFER_PADDING_SIZE);
     if (!a->bitstream_buffer)
         return AVERROR(ENOMEM);
+    memset(a->bitstream_buffer + buf_size, 0, FF_INPUT_BUFFER_PADDING_SIZE);
 
     if(avctx->codec_id == CODEC_ID_ASV1)
         a->dsp.bswap_buf((uint32_t*)a->bitstream_buffer, (const uint32_t*)buf, buf_size/4);