vmd: drop incomplete chunks and spurious samples

Odd chunk size makes no sense for stereo and incomplete chunks are
not supported.

Reported-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
CC: libav-stable@libav.org

libavcodec/vmdav.c

@@ -586,6 +586,9 @@ static int vmdaudio_decode_frame(AVCodecContext *avctx, void *data,
     /* ensure output buffer is large enough */
     audio_chunks = buf_size / s->chunk_size;
 
+    /* drop incomplete chunks */
+    buf_size     = audio_chunks * s->chunk_size;
+
     /* get output buffer */
     frame->nb_samples = ((silent_chunks + audio_chunks) * avctx->block_align) /
                         avctx->channels;
@@ -598,7 +601,8 @@ static int vmdaudio_decode_frame(AVCodecContext *avctx, void *data,
 
     /* decode silent chunks */
     if (silent_chunks > 0) {
-        int silent_size = avctx->block_align * silent_chunks;
+        int silent_size = FFMIN(avctx->block_align * silent_chunks,
+                                frame->nb_samples * avctx->channels);
         if (s->out_bps == 2) {
             memset(output_samples_s16, 0x00, silent_size * 2);
             output_samples_s16 += silent_size;
@@ -610,7 +614,7 @@ static int vmdaudio_decode_frame(AVCodecContext *avctx, void *data,
 
     /* decode audio chunks */
     if (audio_chunks > 0) {
-        buf_end = buf + buf_size;
+        buf_end = buf + (buf_size & ~(avctx->channels > 1));
         while (buf + s->chunk_size <= buf_end) {
             if (s->out_bps == 2) {
                 decode_audio_s16(output_samples_s16, buf, s->chunk_size,