avformat/matroskadec: Don't zero unnecessarily

It is only necessary to zero the initial allocated memory used to store
the size of laced frames if the block used Xiph lacing. Otherwise no
unintialized data was ever used, so use av_malloc instead of av_mallocz.

Also use the correct type for the allocations.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavformat/matroskadec.c

@@ -2788,7 +2788,7 @@ static int matroska_parse_laces(MatroskaDemuxContext *matroska, uint8_t **buf,
 
     if (!type) {
         *laces    = 1;
-        *lace_buf = av_mallocz(sizeof(int));
+        *lace_buf = av_malloc(sizeof(**lace_buf));
         if (!*lace_buf)
             return AVERROR(ENOMEM);
 
@@ -2800,7 +2800,7 @@ static int matroska_parse_laces(MatroskaDemuxContext *matroska, uint8_t **buf,
     *laces    = *data + 1;
     data     += 1;
     size     -= 1;
-    lace_size = av_mallocz(*laces * sizeof(int));
+    lace_size = av_malloc_array(*laces, sizeof(*lace_size));
     if (!lace_size)
         return AVERROR(ENOMEM);
 
@@ -2810,6 +2810,8 @@ static int matroska_parse_laces(MatroskaDemuxContext *matroska, uint8_t **buf,
         uint8_t temp;
         uint32_t total = 0;
         for (n = 0; res == 0 && n < *laces - 1; n++) {
+            lace_size[n] = 0;
+
             while (1) {
                 if (size <= total) {
                     res = AVERROR_INVALIDDATA;