Fixed invalid writes in wavpack decoder on corrupted bitstreams.

Signed-off-by: Martin Storsjö <martin@martin.st>
(cherry picked from commit 0aedab0340)

Signed-off-by: Anton Khirnov <anton@khirnov.net>

libavcodec/wavpack.c

@@ -1113,7 +1113,7 @@ static int wavpack_decode_block(AVCodecContext *avctx, int block_no,
             int16_t *dst = (int16_t*)samples + 1;
             int16_t *src = (int16_t*)samples;
             int cnt = samplecount;
-            while(cnt--){
+            while(cnt-- > 0){
                 *dst = *src;
                 src += channel_stride;
                 dst += channel_stride;
@@ -1122,7 +1122,7 @@ static int wavpack_decode_block(AVCodecContext *avctx, int block_no,
             int32_t *dst = (int32_t*)samples + 1;
             int32_t *src = (int32_t*)samples;
             int cnt = samplecount;
-            while(cnt--){
+            while(cnt-- > 0){
                 *dst = *src;
                 src += channel_stride;
                 dst += channel_stride;
@@ -1131,7 +1131,7 @@ static int wavpack_decode_block(AVCodecContext *avctx, int block_no,
             float *dst = (float*)samples + 1;
             float *src = (float*)samples;
             int cnt = samplecount;
-            while(cnt--){
+            while(cnt-- > 0){
                 *dst = *src;
                 src += channel_stride;
                 dst += channel_stride;