vmdaudio: fix invalid reads when packet size is not a multiple of chunk size

CC:libav-stable@libav.org

libavcodec/vmdav.c

@@ -627,7 +627,7 @@ static int vmdaudio_decode_frame(AVCodecContext *avctx, void *data,
     /* decode audio chunks */
     if (audio_chunks > 0) {
         buf_end = buf + buf_size;
-        while (buf < buf_end) {
+        while (buf + s->chunk_size <= buf_end) {
             if (s->out_bps == 2) {
                 decode_audio_s16(output_samples_s16, buf, s->chunk_size,
                                  avctx->channels);